yes, we can certainly find joy even in His Passion. As I have learned, some of NonCatholics think that we hardly thought about Jesus’ Resurrection. That is very wrong. We proclaim it at every mass, our prayers, the rosary, etc …
His Resurrection us gives us great Hope of eternal life.
Of course, how could we have the full knowledge of how God loves us, but this doesn’t mean we try to avoid to remember how He loves us. What Jesus went through is exactly what Jesus Did for us.
Why Jesus had to suffer physically, besides mentally, for our sins . Sins are to ruins our souls.
As a son, I always want to remember how much my mom did for me. I want to remember how much suffering and hardship she had gone through.
As a Christian, one can always want to know, with God’s help, how much Jesus has suffered for us. The more we know, the more you want to do anything for Christ and the more you ask God to help you stay away from sins.
You are right. What He did - died like a criminal on the Cross and free us from sin - is what we are thankful for.