Why cannot I follow thee now? By these words Peter declares that he was dissatisfied with Christ's answer. He is aware that he has been warned of his own weakness, from which he concludes that it is his own fault that hinders him from following Christ immediately; but he is not at all convinced of it, for mankind are naturally puffed up with confidence in their own value. This expression of Peter shows the opinion which we entertain from our very birth, which is, that we attribute more to our own strength than we ought to do. The consequence is, that they who can do nothing venture to attempt every thing, without imploring the assistance of God.

Why cannot I follow thee now? - Peter probably thought that our Lord intended to go some long journey, which would necessarily subject him to many inconveniences and fatigue; and he felt quite disposed to follow him in this supposed journey, at all hazards. He saw no reason, because he did not see our Lord's meaning, why he could not follow him now.
I will lay down my life for thy sake - Poor Peter! thou wast sincere, but thou didst not know thy own strength. Thou wast at this time willing to die, but when the time cams wast not able. Christ must first die for Peter, before Peter can die for him. Let no man think he can do any thing good, without the immediate assistance of God. Peter's denial should be an eternal warning to all self-confident persons: though there be sincerity and good will at the bottom, yet in the trial these cannot perform that office which belongs to the power of God. We should will, and then look to God for power to execute: without him we can do nothing.

Peter said unto him,.... Not understanding Christ's answer, and being dissatisfied with it, inquires:
Lord, why cannot I follow thee now? is the place inaccessible? are the difficulties in the way to it insuperable? the roughness of the road, or the dangers of it, will not discourage me; I am ready to go through the greatest dangers and difficulties, to follow thee: yea,
I will lay down my life for thy sake; whatever enemies I should meet with in, following thee, would not dismay me; I would readily hazard my life, and cheerfully lay it down in defence of thee.

why not . . . now? I will lay down my life for thy sake--He seems now to see that it was death Christ referred to as what would sever Him from them, but is not staggered at following Him thither. Jesus answered,