Then a cloud came, casting a shadow over them; from the cloud came a voice, "This is my beloved Son. Listen to him." (Mk 9:2-10)
https://bible.usccb.org/bible/readings/022524.cfm
The Transfiguration proclaims that the Law and the Prophets find their fulfillment in the beloved Son. The problem has always been one of failing to listen to him.