When we are transformed by Jesus, this means that everything we have been in the past has already been changed, because we made a decision and that decision was the best, that of following Christ.
The transformation is that which we receive when we decide to open our hearts so that God enters and does what He wants in us, this change allows us to forget everything we once practiced, everything that we were. But God came and changed us.
And was transfigured before them: and his face did shine as the sun, and his raiment was white as the light.
The transfiguration of Jesus was amazing, as verse 2 of chapter 17 of the book of Matthew tells us where Jesus shined like the brightness of the sun, this event was wonderful.
All those who were there witnessing that great miracle, that never seen feat, were completely surprised.
And not only the book of Matthew talks about transformation, throughout the Bible we can find many characters that were transformed.
But we all, with open face beholding as in a glass the glory of the Lord, are changed into the same image from glory to glory, even as by the Spirit of the Lord.
2 Corinthians 3:18
Here we can see the expression of the writer of the second letter to the Corinthians making a clarification of how we can contemplate the beauty of Jesus, and seeing this marvelous glory and splendor, we are completely transformed, when looking with open face His majesty, His power.
When we come before God, we must ask that our whole being be changed and that His grace descend upon each one according to His will. If we believe all this will be possible, because God called us to change, so that we can also lead others to that change and that sublime grace that comes from God.