Matthew 17:3

Moses and Elias. Evidently the disciples recognized the heavenly visitants either from their conversation or by divine illumination. Moses was the great deliverer, lawgiver, and founder of the Hebrew nation, and Elijah the one who saved it in a time of great apostasy and crisis. Here were living representatives to bear witness to the divinity of Jesus, even as “Moses and all the prophets,” through their written records, had testified of Him (see on Luke 24:44).

It is important to note that regarding both Elijah (see on 2 Kings 2:11, 12) and Moses (see on Jude 9) the Scriptures record the fact that the one was translated to heaven without seeing death and the other raised from the dead. The fact that Moses and Elijah appeared with Christ at this time is therefore not to be taken to prove that all the righteous dead are in heaven. These two, one raised from the dead and the other translated without seeing death, appeared with Jesus, as a type of the glorious kingdom in which the ransomed of all ages will be with Him in glory (see Matt. 25:31; Col. 3:4; 1 Thess. 4:16, 17).

Talking with him. Luke adds that they were talking about “his decease which he should accomplish at Jerusalem” (Luke 9:31; cf. Matt. 16:21).