Six days previously, Jesus told the disciples that some of them would not die until they had seen Him in His glory (Matthew 16:28). So soon was the promise fulfilled. He took the three men who would become the leading apostles to show them something of His supernatural nature. Why just three? They were to be eye witnesses who all saw and heard the events on that mountain; and were confident to give that evidence to the Early Church.
 
The rules of evidence were established by God in Deuteronomy 17:6 and 19:15. Hearsay evidence could not be considered, nor the testimony of one person: two or three people must be able to agree on what they witnessed. The glory of Jesus Christ (before His incarnation, after His ascension and at His Second Coming) is such an important part of the gospel that the church would need to be fully assured that Jesus shares the glory of the Father as evidence of His divinity.
 
Peter writes about this in 2 Peter 1:16-18: "For we did not follow cleverly devised stories when we told you about the coming of our Lord Jesus Christ in power, but we were eye-witnesses of his majesty. He received honour and glory from God the Father when the voice came to him from the Majestic Glory, saying, 'This is my Son, whom I love; with him I am well pleased.' We ourselves heard this voice that came from heaven when we were with him on the sacred mountain."
 
Many people today would like to discredit Jesus and the Bible in order to free themselves of any responsibility to submit to Him. Jesus was preparing His apostles to counter those arguments and protect the church from them. This episode in His ministry was designed to answer the question, "Is Jesus the glorious God and King of Heaven?” Yes! The evidence of the three men was conclusive. And so we should be much more confident of the historical accuracy of the Biblical accounts of Jesus. Our faith must be built on facts and not feelings. As we seek to encourage other people, do not get side-tracked away from the historical evidence, but let the Word of God continue to speak its undiluted truth.