“And there appeared unto them Elias with Moses: and they were talking with Jesus.”
Mark 9:4 — Greek Interlinear
Church Fathers on Mark 9:4
After the consummation of the cross, the glory of the resurrection is shewn, that they, who were to see with their own eyes the glory of the resurrection to come, might not fear the shame of the cross.
And He takes with Him the three chief of the Apostles, Peter, as confessing and loving Him, John, as the beloved one, James, as being sublime in speech and as a divine; for so displeasing was he to the Jews, that Herod wishing to please the Jews slew him.
Our Saviour then when transfigured did not lose the substance of real flesh, but shewed forth the glory of His own or of our future resurrection; for such as He then appeared to the Apostles, He will after the judgment appear to all His elect.