One of the significant details of the story that is unique to the account of the transfiguration in Luke 9:28-36, [37-43a] is that it occurs in the context of prayer. We’re told that neither Matthew nor Mark mentions that Jesus had gone up on the mountain specifically to pray and neither mentions that Jesus was praying when the transfiguration occurs. This is clearly a point that Luke wants to make.
In reading Luke during the past few weeks, we recognize that prayer is a significant theme throughout his writings. Luke is the only Gospel author to tell us of Jesus praying on this and other momentous occasions. We remember that following his baptism, the Holy Spirit descended on Jesus while he was praying and perhaps most notably we recall his praying in the garden before his arrest and during his crucifixion.
A point that we may observe in the transfiguration and present in other places, is that prayer for Jesus was not merely speaking words to God but was a spiritual experience of God.
And how do we pray? “…We think of prayer as thoughts of feelings expressed in words, but this is only one of its forms…The Spirit speaks to our conscience through scripture and through events of our daily life. Jesus took the three disciples who were best prepared to receive the grace of contemplation…The voice from heaven awakened their consciousness of the presence of the Spirit who had always been speaking with them, but whom until then, they had never been able to hear...All true prayer is based on the conviction of the presence of the Spirit in us and of his unfailing and continual inspiration.” (Thomas Keating, Open Mind, Open Heart)