Summary: The Cross and the Resurrection are inseperable
The season of Lent stresses a SOMBER mood by having us focus more on fasting and penance. On the other hand, the Gospel tells us about Jesus' Transfiguration [T], where the Lord is seen in full splendor, which seems to be more appropriate for the Easter season. Having the story of the [T] at this time then feels JARRING because the message of the [T] seems to conflict with the spirit of the Lent. It feels like having stayed in a dark cave for many days and then forced to come out into the bright sunlight. Light has very little weight, but it can knock us off our feet if we've become attuned to being in darkness for a while. Having the story of the [T] then seems to be OUT OF PLACE.
How do we explain this? We can better understand a particular passage from the Bible by looking at the passages that come before and after it. For example, the story of Jesus [JC] rebuking Peter for trying to dissuade him from going to Jerusalem to suffer and die on the cross comes before the story of the [T]. We see how Satan is speaking through Peter to prevent Jesus from suffering and dying on the cross to redeem the world. [Here's a good example of how the Devil likes to show himself as an angel of light.] Afterward, JC tells his disciples that if they wished to follow him, then they too should take up their cross.
In his [T], JC then wants to STRONGLY REINFORCE the truth that the way to glory is through the cross, just as he pointed out to Peter in the passage before the [T]. Moses, who represents the Law, and Elijah, who represents the prophets, then UPHOLD this truth by attesting that suffering is redemptive and can lead us to heaven since Moses and the prophets were also persecuted.
JC wants to show his disciples that the sufferings of the Cross, which represents LENT, and the [T], which represents the glory of the Resurrection are INSEPARABLE. Joy and suffering then don't have to be mutually exclusive but should be held in tension out of a love for God. Being joyful during difficult times while being grounded in our trust in Jesus, therefore, is the secret to happiness, which can only come from living a life grounded on supernatural faith. Difficult moments are then actually blessings in disguise because they provide opportunities for us to be humble while keeping faith in God's love for us. We certainly can't attain this strength by our own power. Nonetheless, JC gives his disciples a glimpse of glory to give them HOPE in facing hardships and persecutions. Similarly, JC gives us hope through our daily life, either through the people we meet or situations that he allows us to experience.
God is aware of our needs, so he gives us the consolation to bear our cross. However, we should bear in mind that it's the cross—not consolations—that eventually makes it possible to have eternal life. In other words, the consolations that the Lord gives us helps us to get through the rough times in this world, but it's loving others especially when it's hard to do so that gets us over to the next.
The Gospel then invites us to be transfigured in Christ in bearing hardships with love for God by practicing forgiveness and patience towards one another, just as JC did for us on the cross.