His appearance was as lightning, and his raiment white as snow:
His face blazed with the brightness of lightning itself. The angel wore white as a sign of his own purity and innocence, and to mark Christ's triumph over death; the Jews well knew that God's ministering angels appear clothed in white, so the women would recognize him as a messenger of good, not evil.
AI summary
When Matthew says his countenance blazed like lightning, he means the whole being of the angel shone with peculiar brightness. White garments signaled purity and innocence to the Jewish mind, and celestial beings are always dressed so.
AI summary
His 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.