His countenance - In our language the word "countenance" refers to the "face only;" in the original it refers to his "whole person." His "general aspect, or the appearance of the angel himself," was, etc.
Like lightning - Peculiarly bright and shining.
His raiment white as snow - Celestial beings are usually represented as clothed in white, Acts 1:10; Daniel 7:9; Revelation 3:4-5; Revelation 4:4; Revelation 7:13-14. White, among the Jews, was the symbol of "purity or innocence."

His countenance - His appearance, ἡ ιδεα αυτου; or, his face, for so the word is used in some of the best Greek writers. It seems, from Mark 16:5, that this angel had assumed the appearance of a young man.
Like lightning - Coruscations of glory continually flaming from his face. This might produce the confusion mentioned Matthew 28:2.
His raiment white as snow - He was clothed in garments emblematical of the glad tidings which he came to announce. It would have been inconsistent with the message he brought, had the angel appeared in black robes, such as those preposterously wear who call themselves his successors in the ministry of a once suffering, but now risen and highly exalted, Savior. But the world is as full of nonsense as of sin; and who can correct and bring it to reason and piety?

His (c) countenance was like lightning, and his raiment white as snow:
(c) The beams of his eyes, and by the figure of speech called synecdoche, this is understood as the countenance.

His countenance was like lightning,.... There was such a lustre and brightness in his face, that it glittered like lightning: such a description is in Daniel 10:6,
and his raiment white as snow: the word "white" is left out in the Vulgate Latin, and in Munster's Hebrew Gospel: the angel appeared clad in white, as a token of the purity and innocence of his nature; and because of the victory and triumph of Christ over death and the grave; and that he might be known and taken by the women for a good angel, it being a commonly received notion of the Jews, that ministering angels were clothed in white (b).
"Said R. Ame to R. Levi, show me the Persians; he said to him, they are like to the mighty men of the house of David: show me the Chaberin, (another nation near the Persians,) they are like to destroying angels: show me the Ishmaelites, they are like to devils of the house of Hacsa: show me the disciples of the wise men in Babylon, they are like to the ministering angels.''
Upon which the gloss says,
""to the devils", because they are clothed in black, and are like to devils; to "the ministering angels", "they are clothed in white", and veiled like the ministering angels; as it is written in Ezekiel 9:2, "and the man was clothed with linen": and it is said (c) of R. Judah, that he was veiled, and sat in fine linen fringed, and was like to an angel of the Lord of hosts: and elsewhere (d) it is said, who are the ministering angels? the Rabbins: and why are they called ministering angels? because they are fringed, as the ministering angels, in beautiful garments.''
(b) T. Bab. Kiddushin, fol. 72. 1. (c) T. Bab. Sabbat, fol. 25. 2. (d) T. Bab. Nedarim, fol. 20. 2.

His countenance--appearance.
was like lightning, and his raiment white as snow--the one expressing the glory, the other the purity of the celestial abode from which he came.

His countenance was like lightning. Was bright like lightning. Compare Exodus 34:29; Matthew 17:2; Revelation 1:14.
And his raiment white as snow. White is the emblem of purity. So was the Savior's raiment at the Transfiguration, and the robes of the saints as described in Revelation.