New Defender's Study Bible Notes
9:30 Moses and Elias. This was a vision (Matthew 17:9), rather than an actual bodily visitation. This was prior to the resurrection of Old Testament saints (Matthew 27:51-53), so Moses’ body was still in the grave.
9:31 accomplish. Note that Jesus regarded His approaching death as something He would accomplish. The same word is often translated “fulfill” or “complete.” Although Matthew (17:1-8) and Mark (9:2-8) both report on the transfiguration, only Luke indicates that the approaching death of Christ was the subject He discussed with Moses and Elijah in this vision. Presumably, in his research, Luke was able to elicit this information from one of the disciples who was there—most likely John. Mark presumably got his information from Peter, but doesn’t mention this part of the conversation. Perhaps in his sleepy confusion Peter was too preoccupied with his notion of making three tabernacles (Luke 9:33) to catch these particular words. In any case, this was a vision (Matthew 17:9), so the conversation was to inform Jesus (in His human understanding) of the details of the great work He and His Father were soon to accomplish in Jerusalem.