There talked with him (συνελαλουν αυτω). Imperfect active, were talking with him.

Who appeared in glory (ο οφθεντες εν δοξη). First aorist passive participle of οραω. This item peculiar to Luke. Compare verse Luke 9:26.

Spake of his decease (ελεγον την εξοδον). Imperfect active, were talking about his εξοδυς (departure from earth to heaven) very much like our English word "decease" (Latin decessus, a going away). The glorious light graphically revealed Moses and Elijah talking with Jesus about the very subject concerning which Peter had dared to rebuke Jesus for mentioning (Mark 8:32; Matthew 16:22). This very word εξοδυς (way out) in the sense of death occurs in 2 Peter 1:15 and is followed by a brief description of the Transfiguration glory. Other words for death (θανατος) in the N.T. are εκβασις, going out as departure (Hebrews 13:7), αφιξις, departing (Acts 20:29), αναλυσις, loosening anchor (2 Timothy 4:6) and αναλυσα (Philippians 1:23).

To accomplish (πληρουν). To fulfil. Moses had led the Exodus from Egypt. Jesus will accomplish the exodus of God's people into the Promised Land on high. See on Mark and Matthew for discussion of significance of the appearance of Moses and Elijah as representatives of law and prophecy and with a peculiar death. The purpose of the Transfiguration was to strengthen the heart of Jesus as he was praying long about his approaching death and to give these chosen three disciples a glimpse of his glory for the hour of darkness coming. No one on earth understood the heart of Jesus and so Moses and Elijah came. The poor disciples utterly failed to grasp the significance of it all.