The Lord had begun warning his disciples about the dangers they would face, and also about His Passion and death. He also told them that they would be persecuted by pagans and enemies of the Gospel. He explained that these things pertain to the present life, but what is essential is eternal life. Desiring to give His disciples a foretaste of eternal life, he took three of them, Peter, James and John, and brought them up to Mount Tabor.
There He was transfigured before them and His face shone like light. Moses and Elias appeared and spoke with Jesus. The Lord took only those disciples because they were more pre-eminent than the others. Peter was chosen because he loved Christ very much, John because he also loved Christ, and James because he was able to drink the cup that Christ drank (Matthew 20:23). The Lord showed them Moses and Elias in order to correct their erroneous ideas of who He was, as though He were Saint John the Baptist, or some great prophet. That is why He revealed His glory to them ‘as far as they could bear it.’ All this took place during the Transfiguration of our Lord Jesus Christ on Mount Tabor.