"And a voice came out of the cloud, saying, 'This is My Son, My Chosen One; listen to Him!'"
I have to explain this one, it is so awesome. Jesus is transfigured beside Moses and Elijah as the Father speaks this. Moses and Elijah signify the Law (Genesis through Deuteronomy) and the Prophets (Joshua through Malachi, minus the Writings like Psalms, Proverbs, etc.).
Well, the Father quotes 3 portions of the Old Testament,
one from the Law:
"Yahweh your God will raise up for you a prophet like me [Moses] from among you, from your brothers - it is to Him you shall listen" (DEut 18:15)
one from the prophets:
"Behold My servant, whom I uphold, My chosen, in whom My soul delights" (Isa 42:1)
and one from the Writings:
"I will tell of the decree: Yahweh said to Me, 'You are My Son; today I have begotten You" (Psalm 2:7).
One thing I didn't think of until now: Moses and Elijah are present as witness to Deut 18 and Isa 42 (Elijah the first of the prophets). But who is witness to David's Psalm 2? Maybe it is Jesus Himself, the Son of David...