Because OEC are trying to have the spiritual bend to the temporal rather than have the temporal bend to the spiritual. 1) MACRO-Evolution isn't science-it's a worldview. (MICRO-Evolution, which does occur, is simply genetic variation within a kind...it is how we get different shapes, sizes & colors of each kind). So there is NO reason to find some way to compromise with the world, even on long ages. 2) Do you think that after the implementation of the mark of the beast, anyone who follows the Lamb whithersoever He goes, is going to be holding to any contradictions of Genesis? Of course not....SO why waste time with evolutionary false timescales on this side of the mark of the beast? 3) God re-wrote the creation story as literal in stone, with His own finger, in the 4th commandment.

I think, quite simply, old Earth creationists are trying to reconcile a belief in the Bible with evolutionary theory.

It is difficult to see how anyone could read Genesis without any previously conceived ideas and conclude that the Earth is billions of years old. The plain, literal meaning is that the Earth was created in six 24-hour days several thousand years ago.

That said, in fairness, the most obvious reading is not necessarily the correct reading.

So given a conflict between the plain literal meaning and the popular scientific theories of the day, we have three possible conclusions: (1) The Bible must be wrong, and we must abandon Christianity, or at least any form of Christianity that relies on the Bible for inspiration. (2) The popular scientific theories are wrong, and further research will ultimately vindicate the Bible. (3) We are misreading the Bible, and we must carefully study the text to find alternate readings that are consistent with the popular theories.

Atheists and some liberal Christians take conclusion #1, Biblical literalists take #2, and people like old Earth creationists take #3.

When I was a teenager, I was taught about evolution and concluded that the Bible must be wrong. Like OECs, I looked for a way to re-interpret the Bible. But then I took to studying creation theory, and the more I studied, the more I concluded that the Bible was right and the evolutionists wrong. This isn't an appropriate place to go through all the technical issues, so let me just leave it there. If someone examines the evidence and is convinced that evolution is true, or if he doesn't examine the evidence and just believes what his teachers told him or what he sees on television, than he is going to have to conclude that if the Bible is true, it must be in some allegorical sense, not literal, and he will have to "reinterpret" Genesis.

Update in response to this comment:

Something other than the Sun created the light for the first few days of creation; why should the duration of light from that source be expected bear any relationship to the localized day/night cycles caused by the relative motions of the Earth and Sun later on? — supercat

In principle, who knows? But by the same token you could say, Who says that God didn't change the relative motions of the Earth and Sun at some other time during creation week, or any time since? As the text does not spell out the details we can only speculate. (The text is only a couple of pages. It could hardly be expected to explain all the details of everything that happened. And if it had, 99% of it would have involved science incomprehensible to the people of the time, and 97% of it would have involved science incomprehensible to people today.)

As there was day and night, either the Earth was rotating while the light came from one direction, or the impinging light was, really or effectively, coming from a source orbiting the Earth. Or maybe some combination thereof.

My theory, for what it's worth, is that God created the Earth and set it rotating, and he created a stream of photons with no source to provide light, coming from a single direction, until he created the Sun. When he created the Sun, it then provided the ongoing photon stream, perhaps dropped into place in perfect synchronization. I see this as very similar to the way I develop computer systems. Very often I manually create a data stream when I want to test the consumer of the data stream before I create the source. In some cases I create a temporary "scaffold" program to produce the data stream and later replace it with the real source. Either way, at that point I stop creating the data manually or turn off the temporary program.

It seems plausible that if God did originally set the Earth rotating, that he would have set it rotating at the same speed that he intended it to go in the long term. It seems unlikely to me that he would have it traveling in an orbit around a not-yet-existent Sun. I'd imagine he began the orbit after he created the Sun. If my hypothetical photon stream was coming from a fixed direction, and the Earth was original rotating at the same speed as today, then the day would have been 6 minutes shorter, the difference between a solar day and a sidereal day. (If you're not familiar with that concept, let me know and I can explain. If you care.)

Of course all of this, especially that last paragraph, is a lot of speculation based on very little information. I certainly wouldn't gamble large sums of money on it being right. It is, in my opinion, the most plausible theory based on the available information. There are many other theories that are also quite plausible.

What if the Old Earth view was the more literal view? Remember that the ancient Jews who wrote this defined a day based on the sun. When a day started or ended depended on what time the sun sets. This is much earlier in the Winter than in the Summer, for example. With that in mind, the first couple "days" don't make much sense as a 24-hour period at all, as the sun either did not yet exist, or was at least not yet visible. This implies that a different reading of the text may be in order.

If the author (e.g., the human author) meant to be writing figuratively, or poetically, or even mythically, then in theological parlance, the figurative, poetic, mythic interpretation is the literal interpretation. In theology, it goes by authorial intent, not by high school literature course canons. E.g., St. Augustine talks about 'ages' instead of days, but says this is a literal interpretation. So the word literal, in theology, does not mean what the word 'literal' means in common English modern conversation, nor should it.

The reason that many would discount a literal interpretation (in the sense of a historical reading) of the books of the Bible is more to do with an acknowledgement that they weren't primarily written with intent to convey history, but to teach us something about God's relationship with us. There's a lot of literary study involved in fleshing out all the various points, but this article is one that I find to have a good description of this reasoning. It is all the Catholic perspective, of course, as the Catholic Church does not tend to hold to such a strict style of interpretation of the writings in the Bible at the effort of creating a timeline of events in history for the sake of a history lesson.

For instance, this is the section entitled Creation of the world:

In an article on Biblical chronology it is hardly necessary in these days to discuss the date of the Creation. At least 200 dates have been suggested, varying from 3483 to 6934 years B.C., all based on the supposition that the Bible enables us to settle the point. But it does nothing of the sort. It was natural that in the early days of the Church, the Fathers, writing with little scientific knowledge, should have had a tendency to explain the days of Genesis, i, as natural days of twenty-four hours. Still, they by no means all did so. Thus the Alexandrian Fathers (St. Clement, Origen, St. Athanasius, and St. Cyril) interpreted the days of Creation ideally, and held that God created all things simultaneously. So did St. Augustine; and St. Thomas Aquinas hesitated between idealism and literalism. The literal interpretation has now been entirely abandoned; and the world is admitted to be of immense antiquity. Professor Dana declares its age to be fifty millions of years; others suggest figures still more startling (cf. Buibert, "In the Beginning"; Molloy, "Geology and Revelation"; Hummelauer, "Genesis"; Hastings, "Dictionary of the Bible"; Mangenot in Vig., "Dict. de la Bible"; Driver, "Genesis". Perhaps the words of Genesis (i, 2): "The earth was void and empty, and darkness was on the face of the deep", refer to the first phase of the Creation, the astronomical, before the geological period began. On such questions we have no Biblical evidence, and the Catholic is quite free to follow the teaching of science.

I, myself, primarily as a person with a scientific inclination in thought, and one who desires to understand Scripture in the way that I understand it was treated historically, and in the effort to obtain the truth in its purest form, whatever my preconceptions, I share this interpretation of the Bible. While I'm a Catholic, that is more of a happy coincidence, as I formed my approach before learning how the Church at large does it. I accept the disciplines of science to be a part of this quest for the truth, and as such, truth of God passed down by Scriptures, properly understood, should not contradict with the knowledge gained from scientific discoveries, properly deduced. And so I will accept the prevailing view of the scientific community regarding evolution and the formation of the universe.

An interesting side point is that the theory of the Big Bang actually was first proposed by a Catholic priest (Georges Lemaître) and at its proposal, was initially met with skepticism in part because of its perceived relationship with theological ideas such as creation ex nihilo. However, it now is the dominant theory, and through this model (and other techniques) scientists have been able to extrapolate an estimated age of the universe.

TL;DR version

In my New American Bible, a paragraph in the preface to the book of Genesis addresses this issue very succinctly:

The interpreter of Genesis will recognize at once the distinct object that sets chapters 1-11 apart: the recounting of the origin of the world and of man (primeval history). To make the truths contained in these chapters intelligible to the Israelite people destined to preserve them, they needed to be expressed through elements prevailing among that people at that time. For this reason, the truths themselves must therefore be clearly distinguished from their literary garb.

The issue is not that OECs have a "weak faith," but we believe we are taking a more appropriate view of the scripture. Indeed, if the text is written metaphorically (as we believe), then reading it literally is the weaker position.

If you don't want to read my rather long (yet still way too short to pay true justice to this topic) answer, I suggest jumping down to my Conclusion section, for a summary of why I believe the OEC view pays proper respect to scripture, and is the logical view.

The basic arguments (that I'm aware of) to support the OEC interpretation of Genesis, are:

1. Character of God

As I touched on in this answer:

First, an important Biblical principle is found in Psalm 19:1:

The heavens declare the glory of God; the skies proclaim the work of his hands.

God is revealed through His creation.

Second, from Hebrews 6:18:

...it is impossible for God to lie...

Together, I take this to mean that God's creation, and his scripture must be reconcilable. Any (good) science will not contradict any (good) interpretation of scripture.

This is an important backdrop when reading the rest of this answer.

2. Contextual

There are several clues directly in Genesis that the creation account is not meant to be taken literally. Some good examples:

1. "Morning" and "evening" pass before the sun is created. Either the sun literally existed before it was described in Genesis, or there were no literal days until the sun was created. See this question. A third hypothesis is that the early days of creation meant "24 hour periods," and not specifically "days" as we know them now. But then why refer to "evening" and "morning"? Either the word "day" is metaphor, or "evening" and "morning" are metaphor. In any case, this aspect of the creation account cannot be taken completely literally.

   At minimum one of the key words ("sun", "day", and/or "morning/evening") cannot have the same literal meaning it has today.

2. The seventh day never ended. This seems to be an indication that the days are metaphorical, and that we are presently living in the seventh "day." At the very least, it indicates that the 7th day was somehow distinct and special from the 6 others.

3. The Genesis 2 account of creation doesn't precisely agree with the Genesis 1 account of creation, in terms of order of creation. Man appears to be created before plants, then later placed in "the garden."

4. Genesis 2 describes a number of events that happened between the creation of Adam and the creation of Eve:

   • God planted a garden in Eden
   • Adam worked in and cared for the garden
   • Adam named all of the animals

   Working and caring for a garden is clearly not a one-day task. Nor is naming all of the animals, nor discovering, in this process, that none of the animals are suitable helpers for Adam.

3. Textual

I discussed some of this in this answer, but will elaborate further here.

1. The Hebrew word for day (Yom) used in Genesis 1 has many meanings: (a) Some portion of the daylight (hours), (b) Sunrise to sunset, (c) Sunset to sunset, (d) A segment of time without any reference to solar days (from weeks to a year to several years to an age or epoch) [i.e. "In my grandfather's day" or "in the day of the dinosaurs]

   YECs have several arguments for why Yom in this context means 24-hour day, but they all fall short. I'll discuss two here:

   • Claim: The phrase "evening and morning" "is used 38 times in the Old testament, not counting Genesis 1. Each time, without exception, the phrase refers to a normal 24-hour-type day."³

     Response:

     Interestingly, the word "day" (or yom) appears in none of these examples. The word's plural form occurs only in 1 Samuel 7:16. In only a few of the 38 examples do the words "evening" and "morning" appear in the same sentence or verse. The phrase "evening and morning" appears only one time, in Psalm 55:17. David said, "Evening, and morning, and at noon, will I pray" (KJV). However, even this occurrence is of little relevance. The expression being considered--"and there was evening, and there was morning"--appears only in Genesis 1.²

   • Claim: 358 out of 359 times Yom is used in the Bible, outside of Genesis 1 and with an ordinal modifier, it represents a 24-hour day.¹

     Response:

     Only 249 of these uses use the singular form of 'Yom', and all 249 are in the context of human activity.² Genesis 1 is clearly referring to divine activity.

2. "Morning to morning" or "evening to evening" are common ways of denoting days in Hebrew, however the phrasing "and was evening, and was morning" is unique to Genesis 1, which seems to indicate that these days were unique in some special way.³

4. History

Historically, the church has had a very non-dogmatic view on this issue. Most recorded commentary on this issue has approached the matter mostly as a matter of idle musings, and of little or no real spiritual significance.

The portion of Genesis 1 that describes the six creation days receives more commentary from early church scholars than does any other text in the Bible. However, of the approximately 2,000 pages they wrote (a commentary called the Hexameron), only about two pages address the duration of the creation days. Clearly, the early church fathers did not consider the length of these days a major doctrinal point.⁵

Historically, Jewish and Christian scholars have not considered the creation account to mean a 6 literal day creation. The earliest scholars to even address the issue (around 13 B.C) believed that God instantaneously created everything, and that the 6 days were purely figurative of order and completeness.⁵

St. Augustine spoke the most strongly on the matter, saying: "As for these 'days,' it is difficult, perhaps impossible to think--let alone explain in words--what they mean."⁶ and "But at least we know that it [the Genesis creation day] is different from the ordinary day with which we are familiar."⁷

5. Science

There is a plethora of scientific evidence that suggests the world appears to be much older than YECs claim. Although YECs naturally dispute much of this evidence as weak science, but many of these claims require distorting science. I openly admit that science does not have all the answers about the creation of the world yet, and never will. However, that does not change that many of the scientific principles used to date the earth and/or the universe are very hard to dispute.

You specifically asked not for scientific evidence in support of the OEC view, so I won't go into any detail here. That would be well beyond the scope of this site anyway. I'll only mention one example briefly, and further reiterate my point made above about the Character of God--that God does not lie, and that creation reveals Him. Therefore, whatever good science says about the Universe must, IMO, be true, as a true reflection of God through his creation.

The one example I want to mention, is the simple deductive reasoning that gives astronomers an approximate age for the universe of somewhere around 14 billion years. Read the full details here, but the nutshell version is that by using red/blue-shifting, we are able to observe how quickly the universe is expanding. By doing some backwards math, we can calculate that the universe was all at a single point ~14 billion years ago.

I've heard some YECs argue against this by suggesting that light must have traveled faster in the past, giving the universe the appearance of greater age (due to greater distance between galaxies). However, if the speed of light was not constant, the formation of our life-sustaining sun would not be possible. As the 'c' in E=mc² stands for the speed of light, if that changes, then either the E (energy) or m (mass), or both, must also change accordingly. If this theory was right then "either Adam and Eve would have been incinerated by the Sun's trillionfold increase in heat or the elements essential for building their human bodies would not exist."⁸

Another theory is that light travels faster (or takes a short cut) over vast distances in space. This theory came out before much work on Einstein's theory of general relativity, which has since proven this theory implausible.⁹

Conclusion

Believing in an old earth does not at all detract from the authority one believes the Bible holds. It's not a matter of believing that the bible is "wrong"--it's a matter of believing that that prose ought to be interpreted as prose, and that scientific literature ought to be interpreted as scientific literature--and swapping those in either direction detracts from a proper understanding of the thoughts the author intended to communicate.

Interpreting anything too literally is NOT doing it a service, no matter how pure the intentions of the interpretor.

Now, from a scientific perspective, I think it's easy to forgive the early church scholars for interpreting the Genesis creation account without any (meaningful--from a modern perspective) scientific perspective. However, if the YEC position held any weight in terms of literature or hermeneutics, surely these scholars would have picked up on that.

To believe either of the overarching views, a few "concessions" must be made:

To believe in an Old-Earth:

• The Genesis creation account is metaphorical, and not written as a scientific text.
• The flood account is told from the perspective of those writing it, for whom the entire known earth did flood, but not necessarily the entire literal earth.

To believe in a Young-Earth:

• God arbitrarily chooses use words that have practically no meaning ("day," "morning," and "evening" prior to the sun existing)
• God gave Adam super-human powers, or made the 6th day extremely long, or performed some other miracle to allow Adam to name all of the animals in a single day.
• God created the earth with the appearance of age
• God teleported animals to and from the Ark from/to multiple continents
• Well established scientific principles are flatly wrong, despite independent verification by many people (both religions and non-religious) over many years, in some cases over centuries.
• Reconcile personally that these apparent contradictions don't make God a liar

To me, the first set of "concessions" is much easier to make. It only asks me to read literature in the context it was written. It doesn't ask me to believe what would appear, to an external observer, to be a bunch of fairy tales.

Postscript

As a final note, an observation that doesn't necessarily add any weight to the OEC position--so I mention it here, and not in my main arguments:

OEC is much less of a stumbling block for most non-Christians, because it doesn't require them to make what can easily be considered an "absurd" leap of faith, to believe that science is flatly wrong, etc. In the words of Dr. Joshua Zorn:

The worst aspect of YECS teaching is that it creates a nearly insurmountable barrier between the educated world and the church.⁴

¹Mark Van Bebber and Paul S. Taylor, Creation and Time: A Report on the Progressive Creationist Book by Hugh Ross p. 73
²Hugh Ross, A Matter of Days, p. 74
³Ross, p. 76
⁴Dr. Joshua Zorn, The Testimony of a Formerly Young Earth Missionary
⁵Ross, p. 42
⁶Aurelius Augustinus, The City of God, Book XI, Chapter 6, 14:196
⁷Aurelius Augustinus, The Literal Meaning of Genesis, Book Five, Chapter 2, as translated and anotated by John Hammond Taylor, vol. 1, books 1-6 p. 148
⁸Ross, p. 165
⁹Ross, p. 166