Matthew 17:3
And behold, Moses and Elijah appeared to them, talking with him. The appearance of Moses and Elijah — the great representatives of the Law and the Prophets — communicates that Jesus is the fulfillment of both. Luke 9:31 reveals that their conversation concerned Jesus' exodus (departure) which he was about to accomplish in Jerusalem — connecting the transfiguration directly to the passion that Matthew 16:21 has just predicted. Moses and Elijah are conversing with the one toward whom all their work pointed.