The era of the transfiguration was AD 33 or 33 CE during the last few weeks of Jesus’ life, prior to the crucifixion. Jesus began preaching and gathering followers around CE 28–29. According to the three synoptic gospels Jesus continued preaching for at least one year, and according to John the Evangelist for three years. Five methods have been used to estimate the date of the crucifixion of Jesus. One uses non-Christian sources such as Josephus and Tacitus. Another works backwards from the trial of the Apostle Paul by the Roman proconsul Gallio in Corinth in AD 51/52 to estimate the date of Paul's conversion. Both methods result in AD 33 of the crucifixion, which places the transfiguration within weeks before the passion of Christ.
“And after six days Jesus taketh Peter, James, and John his brother, and bringeth them up into an high mountain apart, And was transfigured before them: and his face did shine as the sun, and his raiment was white as the light. And, behold, there appeared unto them Moses and Elias talking with him. Then answered Peter, and said unto Jesus, Lord, it is good for us to be here: if thou wilt, let us make here three tabernacles; one for thee, and one for Moses, and one for Elias. While he yet spake, behold, a bright cloud overshadowed them: and behold a voice out of the cloud, which said, This is my beloved Son, in whom I am well pleased; hear ye him. And when the disciples heard it, they fell on their face, and were sore afraid. And Jesus came and touched them, and said, Arise, and be not afraid. And when they had lifted up their eyes, they saw no man, save Jesus only. And as they came down from the mountain, Jesus charged them, saying, Tell the vision to no man, until the Son of man be risen again from the dead.” Matthew 17:1-8
The three accounts of this event are found in Matthew 17:1-8, Mark 9:2-8, and Luke 9:28-36. The purpose of the transfiguration of Christ into at least a part of His heavenly glory was so that the “inner circle” of His disciples could gain a greater understanding of who Jesus is. Christ underwent a dramatic change in appearance in order that the disciples could behold Him in His glory. The disciples, who had only known Him in His human body, now had a greater realization of the deity of Christ, though they could not fully comprehend it. That gave them the reassurance they needed after hearing the news of His coming death. Symbolically, the appearance of Moses and Elijah represented the Law and the Prophets. But God’s voice from heaven – “Hear Him!” - showed that the Law and the Prophets must give way to Jesus. The One who is the new and living way is replacing the old – He is the fulfillment of the Law and the countless prophecies in the Old Testament. Also, in His glorified form they saw a preview of His coming glorification and enthronement as King of kings and Lord of lords.
The disciples never forgot what happened that day on the mountain and no doubt this was intended. John wrote in his gospel, “And the Word was made flesh, and dwelt among us, (and we beheld his glory, the glory as of the only begotten of the Father,) full of grace and truth.” John 1:14
Peter also wrote of it, “For we have not followed cunningly devised fables, when we made known unto you the power and coming of our Lord Jesus Christ, but were eyewitnesses of his majesty. For he received from God the Father honour and glory, when there came such a voice to him from the excellent glory, This is my beloved Son, in whom I am well pleased. And this voice which came from heaven we heard, when we were with him in the holy mount.” 2 Peter 1:16-18
Those who witnessed the transfiguration bore witness to it to the other disciples and to countless millions down through the centuries.