What does "the old is better" mean in Luke 5:36–39?

Jesus is simply saying that the traditions are not compatible with the scripture.

The Jews has replaced the scriptures with their own traditions. Many among the followers of Jesus were afraid to give up meaningless traditions as they did not want to offend the Pharisees and rulers.

Jesus is explaining that the new wine which is unfermented and fresh, meaning the true teachings of the word of God are not compatible with people who are not born again, who have been containing the old fermented wine of tradition which, many a times contradicted the express command of God.

Thus born again people are new wine skins.

Unconverted people are old wine skins.

New wine is the teaching from the word of God both new and the old testament.

Old wine is the traditions of men which are unnecessary and many a times lay unneeded burdens upon people.

You should note that the old wine is not the old testament. Fit when Jesus said, "search ye the scriptures... fit they are they which testify of me" He was unequivocally talking about the Old Testament.

Then again as Peter says "for Holy men of God spake as they were moved by the Holy Ghost"

And Paul affirms "All scripture is given by the inspiration of God..."

Luke 5:33 is a reference to the past, in which we are told that Jewish tradition required frequent fasting:

Luke 5:33: And they said unto him, Why do the disciples of John fast often, and make prayers, and likewise the disciples of the Pharisees; but thine eat and drink?

Then verses 34-35 takes us to the new, and to what is to come:

Luke 5:34-35: And he said unto them, Can ye make the children of the bridechamber fast, while the bridegroom is with them? But the days will come, when the bridegroom shall be taken away from them, and then shall they fast in those days.

Finally, Jesus explains that the old does not belong with the new: the old must be discarded and. allegorically, new garments or new wine belong with the new. This teaches that the traditions and laws of the Old Testament will not be part of the Jesus' new Testament.

The earliest version of this parable is in Mark 2:21-22, which makes this point and then proceeds to another passage about the corn fields. However, Luke elaborates on the parable, before proceeding to the passage about the corn fields:

Luke 5:37-39: And no man putteth new wine into old bottles; else the new wine will burst the bottles, and be spilled, and the bottles shall perish. But new wine must be put into new bottles; and both are preserved. No man also having drunk old wine straightway desireth new: for he saith, The old is better.

In verse 39, the author of Luke appears to demonstrate that he misunderstood the parable as it appears in Mark, saying "The old is better". Joseph F. Mali (Two Sayings on the "New" and the "Old", page 263) discusses some differing views on why Luke makes this strange addition, with a general consensus that it is an ironic comment on the Jews, who reject the new gospel.

Jesus was actually saying the complete opposite--well, almost--of what you suggest. Now he was not saying that the old is somehow inferior to the new. Rather, he was saying that the old and the new are not compatible. Let me explain.

First, new wine is incompatible with old wineskins. Since "new wine" when it is placed in a wineskin is not finished fermenting completely, it requires from the wineskin some room in which to expand. The carbon dioxide gas which fermenting wine produces makes this expansion necessary. A new (i.e., fresh or not previously used) wineskin allows for this expansion. An old, used wineskin having become dried and brittle has lost its flexibility. Rather than expanding to accommodate the new wine, it simply bursts and the wine is wasted.

Jesus was using an analogy in this teaching. On the one hand, Jesus considered himself and his teaching to be the new wineskin. His approach to religion required considerable room for expansion. The letter of the Law of Moses needed to expand in order to accommodate the spirit of the law.

Recall the section of Jesus' Sermon on the Mount in which Jesus said time and time again,

You have heard that it was said . . . (Matthew 5:21, 27, 31, 33, 38, and 43).

Jesus then cited a several different commanda from the Law of Moses. Each time he cited a law, however, he followed up with these words,

But I say to you . . . (Matthew 5:22, 28, 32, 34, 39, and 44).

Now Jesus was not setting aside "the letter of the law" contained in the Old Covenant; rather, he was expanding the commandments to include "the spirit of the law."

For example, the commandment "Thou shalt not kill" is a perfectly good commandment which deserves to be obeyed by all people everywhere and at all times. Jesus did not set aside that perfectly good commandment. What he did do was to expand that commandment to include one of the root causes of the sin of murder: unbridled anger.

In like manner, Jesus taught that the root cause of adultery (again, a perfectly good commandment) is lustful thinking. To nip the sin of adultery in the bud requires a careful examination of one's thought life. A man may take pride in never having had sex with a woman who is not his wife, but if his mind is filled with adulterous thoughts, is his pride truly justified? Of course not.

[A caveat: Jesus was not saying that lustful thoughts and physical acts of adultery are one in the same. As bad and destructive as lustful thoughts can be, in a sense they are not as serious as actual acts of adultery. Jesus' point was this: thoughts and the deeds are cut from the same piece of cloth. To think they are not related is to deceive oneself.]

Let me conclude with a key verse from John's Gospel, and some thoughts related to the verse:

The Word became flesh and dwelt among us, and we beheld his [i.e., Jesus'] glory, glory of the only begotten of the Father, full of grace and truth (1:14, my emphasis).

I emphasized the words full of grace and truth because I think they encapsulate very well the reason why Jesus' teaching required new, not old, wineskins. Quite simply, Jesus led with grace and followed up with truth.

Moses' law said in essence, "Obey, and you will live." Jesus' message was in essence, "Live, and you will obey." In other words, heartfelt obedience requires a new heart. Once the heart is made alive and transformed, a new and transformed life of obedience follows. Such is the transforming power of the grace of God, and that's the truth!