This was a unique occasion. Jesus was physically changed; His face and clothing were brilliantly white (Matthew 17:2). Father God validated Jesus as His Son. Moses and Elijah were there too, recognisable and talking with Jesus (Matthew 17:3). It was a foretaste of heaven in which Jesus affirmed the previous ministry of the Law and the Prophets. Moses died but Elijah was taken up to heaven alive in a whirlwind, and so represented the church who would die before the Second Coming and those who would still be alive (1 Thessalonians 4:15).
 
It was a wonderful experience and Peter wanted it to last longer. He suggested making shelters (as the Jews did at the Feast of Tabernacles to remember the wilderness wanderings). But there was no time for that. The three trainee apostles were privileged to see a little glimpse of heaven to encourage them in the hard and dangerous ministries which lay ahead of them. It also laid the visual foundation for John's vision of Jesus in Revelation 1:12-16.
 
But heaven had not yet come to earth. It would come, with the glorified Jesus reigning with the glorified church (BC and AD), but not yet. Peter had the right idea in wanting the glory to stay, but he had the wrong timing. He had not understood that the cross of shame must come before the crown of glory. He wanted heaven on earth right there and then. But Father God knew better: until the day of glory the only thing which matters is that we listen to Jesus and learn to obey Him.
 
Many times since then the church has been tempted to desire 'heaven on earth now'. Promises of freedom from physical ills and from poverty have seduced many into following 'big name speakers' whose personal riches increase with their popularity. Some delude themselves that they are now perfect or that no trouble can touch them. It sounds nice but it is not true. The only thing which matters is that we listen to Jesus, repent of not listening previously, welcome Him and learn to serve Him. We also have to take up our cross before we share His crown.