Peter went up ... - The small room in the second story, or on the roof of the house, was the usual place for retirement and prayer. See the notes on Matthew 6:6; Matthew 9:2. Even when there was no room constructed on the roof, the roof was a common resort for retirement and prayer. Around the edge a battlement or parapet was commonly made, within which a person could be quite retired from public view. “At Jaffa, the ancient Joppa,” says Prof. Hackett (lllustrations of Scripture, p. 81), “where Peter was residing at the time of his vision on the house-top, I observed houses furnished with a wall around the roof, within which a person could sit or kneel without any exposure to the view of others, whether on the adjacent houses or in the streets. At Jerusalem I entered the house of a Jew early one morning, and found a member of the family, sitting secluded and alone on one of the lower roofs, engaged in reading the Scriptures and offering his prayers.”
Dr. Thomson (Land and the Book, vol. i. p. 52) says of these roofs, “When surrounded with battlements, and shaded by vines trained over them, they afford a very agreeable retreat, even at the sixth hour of the day - the time when Peter was favored with that singular vision, by which the kingdom of heaven was thrown open to the Gentile world.”
About the sixth hour - About twelve o’clock (at noon). The Jews had two stated seasons of prayer, morning and evening. But it is evident that the more pious of the Jews frequently added a third season of devotion, probably at noon. Thus, David says Psalms 55:17, “Evening and morning, and at noon, will I pray, and cry aloud.” Thus, Daniel “kneeled upon his knees three times a day and prayed,” Daniel 6:10, Daniel 6:13. It was also customary in the early Christian church to offer prayer at the third, sixth, and ninth hours (Clem. Alex. as quoted by Doddridge). Christians will, however, have not merely stated seasons for prayer, but they will seize upon moments of leisure, and when their feelings strongly incline them to it, to pray.