How do “once saved, always saved” advocates explain the Parable of the Sower?

There is a frame of reference issue here that needs to be clarified first. Everything that Jesus said, taught, and did was consistent with a legitimate offer of the Kingdom to the nation of Israel. He never winked and said, “I know you guys are going to blow it so here is the real plan”.

This taken with an understanding of salvation in the Old Testament economy (righteousness imputed according to faith) combines to differentiate salvation from the New Testament economy. We have the example Paul gives us of Abraham;

Romans 4:20-22 He staggered not at the promise of God through unbelief; but was strong in faith, giving glory to God; And being fully persuaded that, what he had promised, he was able also to perform. And therefore it was imputed to him for righteousness.

We can see that those who have the opportunity to specifically trust in Christ receive their new and eternal life in Christ while they are still alive;

John 5:24 Verily, verily, I say unto you, He that heareth my word, and believeth on him that sent me, hath everlasting life, and shall not come into condemnation; but is passed from death unto life.

2 Corinthians 1:22 Who hath also sealed us, and given the earnest of the Spirit in our hearts.

Hebrews 11:39-40 And these all, having obtained a good report through faith, received not the promise: God having provided some better thing for us, that they without us should not be made perfect.

The Old Testament saints receive their new and eternal life at what Revelation calls the first resurrection;

Revelation 20:6 Blessed and holy is he that hath part in the first resurrection: on such the second death hath no power, but they shall be priests of God and of Christ, and shall reign with him a thousand years.

Daniel 12:2 And many of them that sleep in the dust of the earth shall awake, some to everlasting life, and some to shame and everlasting contempt.

This has bearing upon the parable of the sower in that none of the four examples receive new and eternal life at that time so the idea of “once saved always saved could not apply. The metrics to determine which type of person had sufficient faith so that righteousness would be imputed to them is not given.

I am sorry I am not able to quote any published theologian as I am unaware of any who might hold to this differentiation between Old and New Testament saints and thus would be able to consider the application to the parable of the sower.

As with all Scripture it is not possible to take only a part of Jesus teachings alone and understand Salvation, but all of his teachings are a part of gaining access to the Kingdom. Otherwise Jesus would not have taken three years to bring his message to us.

Beginning with the Parable of the sower let us see if we can determine the course for attaining the Kingdom.

This is an excerpt from the commentary by David Guzik:

4. (11-15) Jesus explains the parable.
   "Now the parable is this: The seed is the word of God. Those by the wayside are the ones who hear; then the devil comes and takes away the word out of their hearts, lest they should believe and be saved. But the ones on the rock are those who, when they hear, receive the word with joy; and these have no root, who believe for a while and in time of temptation fall away. Now the ones that fell among thorns are those who, when they have heard, go out and are choked with cares, riches, and pleasures of life, and bring no fruit to maturity. But the ones that fell on the good ground are those who, having heard the word with a noble and good heart, keep it and bear fruit with patience."
   a. The seed is the word of God: 1Pe. 1:23 says that we have been born again, not of corruptible seed but incorruptible, through the word of God which lives and abides forever.
   i. The natural tendency is for the audience to critique the preacher. But here, Jesus the preacher is critiquing His audience. How they will hear is the issue.
   b. Those by the wayside are the ones who hear; then the devil comes and takes away the word out of their hearts, lest they should believe and be saved: Some people are like the ground on the pathway. They allow no room for the seed of the word in their lives - it never enters.
   i. This is Satan's preferred result. His desire is that the word take no place in a person's life, so they do not run the "risk" of being fruitful to God.
   c. But the ones on the rock are those who, when they hear, receive the word with joy; and these have no root, who believe for a while and in time of temptation fall away: Some people are like the ground that is rocky, but covered with a thin layer of topsoil. They receive the seed of the word with a flash of enthusiasm that quickly burns out.
   d. Now the ones that fell among thorns are those who, when they have heard, go out and are choked with cares, riches, and pleasures of life, and bring no fruit to maturity: Some people are like the seed that fell among the thorns. They receive the word but allow the interests and cares of this world choke it out.
   e. The ones that fell on the good ground are those who, having heard the word with a noble and good heart, keep it and bear fruit with patience: Some people are like the good ground, and receive the word with a good and noble heart. They keep the word, and thus bear fruit, thus fulfilling the purpose of the seed.
   f. These four categories apply to those who hear the gospel of salvation, but they also apply to those who are already saved who continually hear the word of God.

As Jesus said this is about people's reception of the word, and does not really speak to whether or not they received salvation.

The following is an excerpt from John Gill's commentary:

Now the parable is this, &c] "Or this is the sense of the parable", as the Arabic version renders it: "the seed is the word of God", the Gospel, as preached by Christ, his apostles, and faithful ministers, which has God for its author, is concerning the grace of God, and is what he blesses, and makes effectual to answer any good purpose.

Those by the wayside are they that hear,.... The word of God, though only by accident, and very carelessly, and without understanding what they hear:

then cometh the devil; signified by the fowls of the air:

and taketh away the word out of their hearts, or memories; that little of it, which is retained there, and diverts their minds from it by other objects; so that they quite forget what they have heard;

lest they should believe, and be saved: this clause is only in Luke; and with it may be compared 2Co 4:4 for with true faith in Christ the sum and substance of the word salvation is connected; and Satan being an enemy to the salvation of souls, does all he can to hinder their faith in him.

They on the rock are they, which when they hear,.... The seed that fell upon the rock, or stony ground, signify such sort of hearers,

who receive the word with joy. The Ethiopic version reads, "with joy of heart". But, this sort of hearers receive not the word into their hearts, or with their hearts believe it, and from their hearts obey it, only into their heads; and have only, an historical faith of it; nor with hearty, spiritual, solid joy, or joy in the Holy Ghost: for their hearts remain like a rock, unbroken by the word; but with a flash of natural affection, which quickly goes off.

And these have no root; neither "in themselves", as the other evangelists say, they have no true grace in them; nor have they any root in Christ, nor in the love of God:

which for a while believe: their faith is a temporary one, like that of Simon Magus; which shows it is not true faith; for that is an abiding grace, Christ, who is the author, is the finisher of it, and prays for it, that it fail not. The Persic version renders it, "in the time of hearing they have faith"; and such sort of hearers there are, who, whilst they are hearing, assent to what they hear, but when they are gone, either forget it, or, falling into bad company, are prevailed upon to doubt of it, and disbelieve it. The Arabic version renders it, "they believe for a small time"; their faith do not continue long, nor their profession of it, both are soon dropped:

and in the time of temptation fall away: "or go back", as the Vulgate Latin version, they draw back unto perdition; or "forsake that", as the Arabic version reads, the word, they have heard, and received, their faith in it, and profession of it: "and soon become apostates", as the Persic version renders it. By "the time of temptation", is not meant any particular and sore temptation of Satan, but a time of affliction and persecution, as appears from the other evangelists; which is a trying time to professors of religion, and when those who have not the root of the matter in them, fall away.

And that which fell among thorns are they,.... The seed that fell among thorns, or were sown on thorny ground, represent such hearers:

which, when they have heard, go forth; from hearing the word to their worldly business; or go on in the pursuit of their worldly lusts and pleasures notwithstanding; for the word translated, "go forth", belongs to the next clause;

and are choked with cares and riches, and pleasures of this life; and with it to be read thus, "and going on in or under", that is, under the power and influence of, "the cares, and riches, and pleasures of life", they are choked; to which agrees the Arabic version, which renders it, "in which they walk", or "which they follow". The Vulgate Latin version is, "and from the cares, and riches, and pleasures of life, going, they are choked": but it is not going from them, but going on in them, which chokes them, or suffocates the word they have heard, whereby it becomes of no effect; unless it should be rendered, "by the cares", c. "they are choked, and bring no fruit to perfection" for what fruit such hearers do bring forth, in a way of profession, soon drops off, and perishes.

But that on the good ground are they,.... The seed that fell on good ground design such hearers,

which in an honest and good heart, having heard the word, keep it: who hear with an honest and good intention, and faithfully keep it, and hold it fast:

and bring forth fruit with patience; with great constancy, suffering much for the sake of it; and the more they suffer, the more fruitful they are.

From Jesus explanation and by dissecting them with the use of these two plus other commentaries we see that it is not just the hearing of the word and the mulling it over in the mind that establishes salvation, but heartfelt acceptance of the fact that Jesus did in fact pay our penalty of death and that that left us sinless. Jesus' explanation of the reception of the word does not tell us where the dividing line between salvation and not being saved intersects the narrative. For instance we do not know whether those who gleefully accept the word and then fall away have received salvation or not. Jesus' sacrifice paid for all the sins of those who receive him, but we do not know if those people will join us in Heaven or not, only Jesus can make that determination.

There are far too many Scriptures dealing with Salvation to enumerate them here, and even Jesus' teachings would turn this into a book. One verse which seems to be quite cogent here though is:

Matthew 10:38 KJV And he that taketh not his cross, and followeth after me, is not worthy of me.

But that does not say they will be denied the Kingdom only that they are not worthy. and another of Jesus' teachings tells us:

Matthew 18:3 and 4 KJV And said, Verily I say unto you, Except ye be converted, and become as little children, ye shall not enter into the kingdom of heaven. 4 Whosoever therefore shall humble himself as this little child, the same is greatest in the kingdom of heaven.

the full answer to your question lies in the Gospels themselves, what opinion any group or individual may have concerning Salvation, is of little value, but how you accept the Gospel is of paramount importance since only Jesus' judgment has any eternal value.

Hope this helps.

(I know the question says good answers will have references from published commentaries; I may look for some later when I get the chance to go to my college library, but for now this answer will be my explanation of the kind of perspective I have heard.)

Those who believe in the perseverance (or preservation) of the saints or eternal security of salvation, view justification as a permanent change of state. Justification is seen as permanent, as the question already clearly says, so I won't go into it. But it must also be understood that our state before God is seen as a binary state, with only two options: we are either justified or we are not. There are several Biblical images for this binary state change:

• being dead vs alive in Christ (Ephesians 2)
• being Jesus' enemy vs being reconciled to God (Matthew 12:30)
• being strangers to God vs being citizens of heaven (Ephesians 2:19)

(I'm not aware of any groups who teach permanent but non-binary justification, but such a system would be theoretically possible. Maybe there could be several steps to take before you are fully saved, and once you move forward a step you can never move back, even though you may not reach the end. Maybe the Catholic understanding of baptism could be understood this way, as you can never become unbaptisted.)

In the parable of the sower the first group is clearly the unjustified, those who reject the message and offer of God. The last group is clearly justified: those who have a healthy Christian faith, pleasing God in their lives. The question is whether the second and third groups are justified. There is debate over these groups, even among those who support the perseverance of the saints. The issue is whether the signs of faith they show are just the illusion of faith, or whether they are real evidences of a life changed through the gospel. The first group "hears" but does not "believe". The second group "receive the word with joy" and "believe". The third group only "hears" it, while the fourth group "hears" or "hears and understands" in Matthew's version.

Jesus frequently indicated that there were different kids of hearing: "He who has ears, let him hear." All four groups hear the gospel, but not all four respond. The second and fourth definitely do, the third is less clear. But when you consider the parable itself, not just the explanation, the seed takes root in all except the first group. So I am someone who interprets this parable as indicating that the second and third groups "receive the word with joy" and "believe": they experience the permanent change of justification. The have received life and the holy spirit, they are adopted as children of God, they are members of the body of Christ.

So lastly, how would I explain their seeming change back into unbelief? We must distinguish between justification and whether a person lives a life that pleases or disappoints God. The key passage for my understanding is 1 Corinthians 3: 12-15, which describes our future judgement before God as our being tested by fire. There are some people whose lives will show little fruit of the gospel, with their works being burnt away, though they themselves will be saved. I believe that the Holy Spirit cannot be stopped from producing good works in those who are saved, but they may produce few, and they may even die without having repented from their apostasy. But if they have been justified, a change only God can know, then regardless of how it seems to the rest of us, that person is saved for eternity.