Matthew 17:2-9: "2 And he [Jesus] was transfigured before them, and his face shone like the sun, and his clothes became white as light. 3 And behold, there appeared to them Moses and Elijah, talking with him. 4 And Peter said to Jesus, 'Lord, it is good that we are here. If you wish, I will make three tents here, one for you and one for Moses and one for Elijah.' 5 He was still speaking when, behold, a bright cloud overshadowed them, and a voice from the cloud said, 'This is my beloved Son, with whom I am well pleased; listen to him.' 6 When the disciples heard this, they fell on their faces and were terrified. 7 But Jesus came and touched them, saying, 'Rise, and have no fear.' 8 And when they lifted up their eyes, they saw no one but Jesus only.
"9 And as they were coming down the mountain, Jesus commanded them, 'Tell no one the vision, until the Son of Man is raised from the dead.'"
2 Peter 1:16: "For we did not follow cleverly devised myths when we made known to you the power and coming of our Lord Jesus Christ, but we were eyewitnesses of his majesty."
+++
There isn't much to say about this one. The hymn is about the Transfiguration, and the text from Matthew is the main Biblical source. The text from 2 Peter is about the same event, but it has a slightly different focus. In the hymn, this appears in the second half of the first verse and all of the second verse, which detail the response that Peter, James, and John have to the Transfiguration ("They shall gain and keep its truth").
