Luke 17:5

And the apostles said unto the Lord,.... Either on account of what was now said by Christ concerning offences, and forgiving injuries; being conscious to themselves of their own weakness to withstand temptations; and fearful lest they should be stumbled and offended with what they should meet with; or that they should give offence to others: and being also sensible of what spirits they were of, and of the difficulties of conquering them, and mastering the resentment of their minds, when injured and provoked; and also the necessity of divine assistance, of having fresh supplies of grace, and of having their graces, and particularly faith, strengthened, and drawn into a lively exercise; or on account of their not being able to cast out a devil from one that was possessed,

Matthew 17:19 when words, to the same purpose, were spoken by Christ, as in the following verse; on occasion of one or other of these, though more likely the former, the apostles addressed Christ in this manner,

increase our faith; both the faith of working miracles, and the grace of believing in him: by which, as they express their sense of the weakness, and imperfection of their faith; and their great desire to have it increased, which might be for their comfort, and his glory; so they acknowledge his divine power, and that he is the author and finisher of faith; and that as the beginning, so the increase of it is from him: wherefore faith is not of a man's self, or the produce of man's freewill and power, but is the gift of God; and even where it is, it is not in man to increase it, or add to it, or to draw it forth into exercise; this also is the operation of God. And if the apostles had need to put up such a petition to Christ, much more reason have other men.