“And was transfigured before them: and his face did shine as the sun, and his raiment was white as the light.”
Matthew 17:2 — Greek Interlinear
Church Fathers on Matthew 17:2
In this Transfiguration undergone on the mount, the Lord fulfilled within six days the promise made to His disciples, that they should have a sight of His glory; as it is said, 'And after six days he took Peter, and James, and John his brother.'
It is made a question how it could be after six days that He took them, when Luke says eight. The answer is easy, that here one reckoned only the intervening days, there the first and the last are also added.
He does not take them up immediately upon the promise being made, but six days after, for this reason, that the other disciples might not be touched with any human passion, as a feeling of jealousy; or else that during these days' space, those disciples who were to be taken up might become kindled with a more eager desire.