So why is Good Friday called Good Friday?
Perhaps the best definition should be the words of the Holy Scripture, "Looking to Jesus, the founder and perfecter of our faith, who for the joy that was set before him, endured the cross, despising the shame, and is seated at the right hand of the throne of God." (Hebrews 12:2)
Joy? Jesus counted being tortured, despised, humiliated, and killed as joy? The answer is yes. For in that moment on the cross, Jesus, the sinless One, took the punishment of all of our sins, so that we could become blameless before God. In that cosmic transformation, He became something He wasn't so that we could become something we couldn't.
Put simply, He died, so we could live.