John Calvin Commentary Acts 10:9

"Now on the morrow, as they were on their journey, and drew nigh unto the city, Peter went up upon the housetop to pray, about the sixth hour:" — Acts 10:9 (ASV)

On the morrow, as they journeyed. Just as Luke declared that Cornelius was admonished by a divine message to send for Peter, so now he records another vision, by which Peter is commanded to come to him. From this it appears that this entire matter was governed by the wonderful counsel of God, who both makes Cornelius receptive to being taught—indeed, He kindles in him a zeal and desire to learn—and, on the other hand, makes Peter willing to undertake teaching him. But we must note the circumstances by which he makes the history more clear.

Peter went up upon the house, so that he might pray alone by himself. For a quiet and solitary place is a great help to prayer, a practice Christ Himself did not neglect, so that the mind, being free from all distractions, might be more earnest and focused on God. The Jews had a different style of houses and buildings than we use, for they had walkways on the tops of their houses. The sixth hour was then noon.

And it is not to be doubted that he went to pray then according to his custom. For since we are drawn away by various affairs, and there is no end to turmoil, unless we discipline ourselves, it is good to have certain hours appointed for prayer. This is not because we are bound to hours, but so that we do not become unmindful of prayer, which ought to be preferred above all cares and business. Finally, we must think the same way about time as we do about place: namely, that they are certain aids by which our weaknesses are helped. If the apostles considered these suitable for themselves, how much more must the sluggish and slow use them?