See this passage illustrated in the notes at Matthew 9:14-17.

And they say unto him,.... The Scribes and Pharisees, or the disciples of John; see Matthew 9:14

why do the disciples of John fast often, and make prayers? set times apart frequently for fasting and prayer. The Ethiopic version reads, "why do the disciples of John baptize frequently, fast, and make prayers?" in which the former clause is added; and as without any authority, so without judgment, since it must suppose that the Pharisees did so likewise, whereas they rejected the baptism of John; for it follows, and "likewise" the disciples of "the Pharisees"; who fasted often, at least twice in the week, and made frequent prayers in the synagogues, and corners of the streets, and in widows' houses.

But thine eat and drink? instead of fasting and praying; See Gill on Matthew 9:14.

Often (πυκνὰ)

Only here, Acts 24:26; 1 Timothy 5:23. The word literally means close-packed, as a thicket, or the plumage of a bird.

Prayers (δεήσεις)

Used by no other evangelist. From δέομαι, to want, and hence distinctively of petitionary prayer. In classical Greek the word is not restricted to sacred uses, but is employed of requests preferred to men. Rev., more correctly, supplications.

{6} 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?

(6) Hypocrites and ignorant men make a point of making fasting and unimportant things a matter of holiness.

5:33 Why do the disciples of John fast? Intended as a rebuke for their attendance at a great feast. Jesus shows that fasting ought not to be form, but to have a meaning.

5:33 Make prayers - Long and solemn. Mt 9:14; Mr 2:18.

Lu 5:33-39. Fasting.

(See on [1577]Mt 9:14-17.)

The incongruities mentioned in Lu 5:36-38 were intended to illustrate the difference between the genius of the old and new economies, and the danger of mixing up the one with the other. As in the one case supposed, "the rent is made worse," and in the other, "the new wine is spilled," so by a mongrel mixture of the ascetic ritualism of the old with the spiritual freedom of the new economy, both are disfigured and destroyed. The additional parable in Lu 5:39, which is peculiar to Luke, has been variously interpreted. But the "new wine" seems plainly to be the evangelical freedom which Christ was introducing; and the old, the opposite spirit of Judaism: men long accustomed to the latter could not be expected "straightway"-all at once-to take a liking for the former; that is, "These inquiries about the difference between My disciples and the Pharisees," and even John's, are not surprising; they are the effect of a natural revulsion against sudden change, which time will cure; the new wine will itself in time become old, and so acquire all the added charms of antiquity. What lessons does this teach, on the one hand, to those who unreasonably cling to what is getting antiquated; and, on the other, to hasty reformers who have no patience with the timidity of their weaker brethren!

5:27-39 It was a wonder of Christ's grace, that he would call a publican to be his disciple and follower. It was a wonder of his grace, that the call was made so effectual. It was a wonder of his grace, that he came to call sinners to repentance, and to assure them of pardon. It was a wonder of his grace, that he so patiently bore the contradiction of sinners against himself and his disciples. It was a wonder of his grace, that he fixed the services of his disciples according to their strength and standing. The Lord trains up his people gradually for the trials allotted them; we should copy his example in dealing with the weak in faith, or the tempted believer.