The Passover affords a more than usually solemn day for baptism; when, withal, the Lord's passion, in which we are baptized, was completed. Nor will it be incongruous to interpret figuratively the fact that, when the Lord was about to celebrate the last Passover, He said to the disciples who were sent to make preparation, "You will meet a man bearing water." He points out the place for celebrating the Passover by the sign of water. After that, Pentecost is a most joyous space for conferring baptisms; wherein, too, the resurrection of the Lord was repeatedly proved among the disciples [Acts 1:3], and the hope of the advent of the Lord indirectly pointed to, in that, at that time, when He had been received back into the heavens [Acts 1:9], the angels told the apostles that "He would so come, as He had withal ascended into the heavens;" [Acts 1:11] at Pentecost, of course. But, moreover, when Jeremiah says, "And I will gather them together from the extremities of the land in the feast-day," he signifies the day of the Passover and of Pentecost, which is properly a "feast-day." However, every day is the Lord's; every hour, every time, is apt for baptism: if there is a difference in the solemnity, distinction there is none in the grace.
After that, Pentecost is a most joyous space for conferring baptisms; wherein, too, the resurrection of the Lord was repeatedly proved among the disciples, and the hope of the advent of the Lord indirectly pointed to, in that, at that time, when He had been received back into the heavens, the angels told the apostles that "He would so come, as He had withal ascended into the heavens; " at Pentecost, of course.
Behold, two men stood by them in white apparel. White garments are more fitting for exaltation than for humiliation. And so, as the Lord ascends, angels appear in white garments, who are not said to appear in white clothing at the Lord's birth, because he who appeared humble as a God in his birth, appeared sublime as a man in his ascension. For the location is also fitting, while he, who was born as a man in a humble little city, returned to heaven from a high mountain.
While they were looking on as he went into heaven. In Greek, it is thus: And while they were gazing into heaven as he went; that is, they were gazing into heaven, where he was going. Hence, the angels say to them: Why do you stand looking into heaven? Because it is also shown that they were gazing at him who was going into heaven, by the angels' following words, when it is said: He will come in the same way you saw him going into heaven.
[AD 220] Tertullian on Acts 1:3-11