Two men He calleth them so by reason of their form. For although it might be that they had the bodies of men in deed, concerning which thing I will not greatly stand in defense of either part, yet certain it is they were not men; but because this metonymia is commonly used in the Scriptures, especially in the First Book of Moses, I will not greatly stand thereupon. Their white garments were a token of rare and excellent dignity. For God meant by this, as by an evident token to distinguish them from the common sort of people, that the disciples might give better ear unto them; [1] and that at this day we also may know that this vision was showed them of God.

Footnotes

1 - "Ad eorum dicta attentiores," might be more attentive to what they said.

Looked stedfastly - They fixed their eyes, or gazed intently toward heaven. Luke 4:20, "and the eyes of all them in the synagogue were fastened (Greek: the same word as here) on him." It denotes the intense gaze when we are deeply interested, and wish to see clearly and distinctly. They were amazed and confounded; what had occurred was unlocked for; for they had just been inquiring whether he would not, at that time, restore the kingdom to Israel. With this mingled amazement, disappointment, and curiosity, and with an earnest desire to catch the last glimpse of their beloved master, they naturally continued to gaze on the distant clouds where he had mysteriously disappeared from their view. Never was a scene more impressive, grand, and solemn than this.
Toward heaven - Toward the distant clouds or sky which had received him.
As he went up - Literally, upon him going up; that is, they gazed on him as he ascended, and doubtless they continued to gaze after he had disappeared from their view.
Two men - From the raiment of these "men," and the nature of their message, it seems clear that they were angelic beings, who were sent to meet and comfort the disciples on this occasion. They appeared in human form, and Luke describes them as they appeared. Angels are not infrequently called people. Luke 24:4, "two men stood by them in shining garments," etc. Compare John 20:12; Matthew 28:5. As two angels are mentioned only as addressing the apostles after the resurrection of Jesus John 20:12; Luke 24:4, it is no unnatural supposition that these were the same who had been designated to the honorable office of bearing witness to his resurrection, and of giving them all the information about that resurrection, and of his ascension, which their circumstances needed.
In white apparel - Angels are commonly represented as clothed in white. See the John 20:12 note; Matthew 28:3 note; Mark 16:5 note. It is an emblem of purity; and the worshippers of heaven are represented as clothed in this manner. Revelation 3:4, "they shall walk with me in white"; Revelation 3:5, "He that overcometh shall be clothed in white raiment"; Revelation 4:4; Revelation 7:9, Revelation 7:13-14.

Looked steadfastly - Keeping their eyes intensely fixed on their ascending Lord; continuing to look even after he had ascended above the region of the inferior clouds.
Two men stood by them - Doubtless, angels in human shape.
In white apparel - As emblematical of their purity, happiness, and glory.

And while they looked steadfastly toward heaven,.... For though he was taken out of their sight by the cloud, they kept looking upwards, and after him, if they could see him again, or any more of him:
as he went up; they looked up to heaven after him, as he went up from the earth, before the cloud took him out of their sight; and still they continued looking, as the cloud carried him up, until it was out of the reach of their sight, being willing to see the last of him in this way:
behold, two men stood by them in white apparel; that is, two angels in the form of men; it being usual with them to appear in human form: these on a sudden appeared and stood on the earth just by them; though the Ethiopic version renders it, "they stood above them", as if they were in the air over their heads; and they appeared in white apparel, as the angel at the sepulchre in Matthew 28:2 which was a symbol both of their purity and holiness, and of their lustre and glory. The Ethiopic version renders it, "they were clothed with lightning"; they appeared in such a dazzling form, that it looked as if they were covered with lightning; as the angel that appeared at Christ's resurrection, his countenance is said to be as lightning; which must at once fix the attention of the disciples to them, and strike them with surprise: hence a "behold" is prefixed to this: and hereby they knew that they were not common and ordinary men, or mere men, but angels in such a form.

while they looked steadfastly toward heaven--following Him with their eager eyes, in rapt amazement. Not, however, as a mere fact is this recorded, but as a part of that resistless evidence of their senses on which their whole subsequent testimony was to be borne.
two men in white apparel--angels in human form, as in Luke 24:4.