"Do not remember the sins of my youth or my transgressions; according to your steadfast love remember me, for the sake of your goodness, O Lord!" Psalm 25:7
This is a question most Christians (and all people!) raise today. The United Methodist Communications Office put out a short video that answers this question. I recommend you watch here.
Goodness and death don't typically collide in the same sentence. Yet we believe that this day means God forgives us and removes our sins through the supreme sacrifice of God's Son, Jesus. I'm not into the wrath of God—that Jesus had to satisfy God's wrath by dying on the cross. I'm not into ransom—that Jesus was the ransom God paid the devil to set us free (yes, that was, and still is, a thing with many Christians). And I'm not all that into substitution—that God needed a substitute sacrifice for the price of our sin. Jesus' desire all along was to take away our sin, to forgive, to set us free. His commitment to this mission of bridging a world to the love and will of God was ultimate, to the point of death.
The cross is not just about personal salvation. It's also about justice and the righting of wrongs that divide and separate us from God's will. As well, the cross is about peace and the restoration of relationships between humanity and one another.
That's about as good as I got for explaining the goodness of this day. I believe the Psalmist says it best, that when it comes to asking God not to remember our sins and transgressions (corporate and individual; the ones we know and don't know) it is according to the goodness of God.
Is it a mystery? For sure. But this mystery is what makes today Good Friday.
See you Sunday when we celebrate an even bigger mystery!