Why did Jesus brought along Peter, John and James to the mountain of Transfiguration? It was for them to see and experience what shall await them if they will not give-up and continue to be faithful to the teachings of Jesus.
It was a foretaste of heaven actually, but before heaven there shall be trials, before heaven there shall be persecutions and before heaven our discipleship might be severely tested. Test and trials are part and parcel of our Christian discipleship no one who choose to follow Jesus is exempt from it.
But after all the trials of our discipleship has been said and done with; there shall be an ecstatic experience of heaven for all of us.
So always be faithful to your discipleship and never allow the temptation of this world to distract you. ...