Luke 9:29

And as he prayed, the fashion of his countenance was altered,
&c.] It became exceeding bright and glorious, it shone like the sun, ( Matthew 17:2 ) and hereby his prayer was answered; and thus, as Christ was heard and answered, whilst he was yet speaking, so are his people sometimes; and even their countenance is altered, when they are favoured with communion with God, and instead of a sad and dejected countenance, they have a cheerful one. And his raiment was white and glistering;
it was as white as the light, as snow, and whiter than any fuller on earth could whiten, as the other evangelists say, and so glistened exceedingly; (See Gill on Matthew 17:2). (See Gill on Mark 9:3).