50 And he led them out as far as Bethania: and lifting up his hands, he blessed them.
Theophylact: Perhaps pouring into them a power of preservation, until the coming of the Spirit; and perhaps instructing them, that as often as we go away, we should commend to God by our blessing those who are placed under us.
Origen: That He blessed them with uplifted hands, signifies that it becomes him who blesses any one to be furnished with various works and labors in behalf of others. For in this way are the hands raised up on high.
Bede: Having omitted all those things which may have taken place during forty-three days between our Lord and His disciples, St. Luke silently joins to the first day of the resurrection, the last day when He ascended into heaven.
51 And it came to pass, whilst he blessed them, he departed from them, and was carried up to heaven. 52 And they adoring went back into Jerusalem with great joy. 53 And they were always in the temple, praising and blessing God. Amen.
Theophylact: Elias indeed was seen, as it were, to be taken up into heaven [2 Kgs 2:11], but the Savior, the forerunner of all, Himself ascended into heaven.
Chrysostom: The Lord submits to our sight the promised rewards. He had promised the resurrection of the body; He rose from the dead, and conferred with His disciples for forty days. It is also promised that we shall be caught up in the clouds through the air; this also He made manifest by His works.
You also shall be taken up in like manner into the clouds. For your body is of like nature to His body, therefore shall your body be so light, that it can pass through the air. For as is the head, so also is the body; as the beginning, so also the end. See then how you are honored by this beginning.
Scripture from the Douay-Rheims Bible. Commentary from St. Thomas Aquinas, Catena Aurea, Vol. III (London: Rivington, 1843).