Crazy how I never understood this before. A Christian's joy and deep comedy happiness comes from giving glory to God. I had thought prior to tonight, in some way, that a believer should rejoice because God loves them and has forgiven them. Yet this isn't perfectly true, and it lacks beauty. It would mean that we rejoice in God because He loves us. In other words, that we honor Him because He makes much of us, that because He makes much of us He is lovely too us. Our loving Him, then, would be dependent on His love for us.
Yet our happiness isn't dependent on how God loves us per se, but how He allows us to love Him. What a change! I can't explain this notion completely as I've just come to the realization myself, but I can tell it has a large impact already. For instance, before this epiphany I have tried to love other people by seeing them as God sees them and loves them, in their place just as they are because they are human. In the new outlook, however, I can really love them for what they could be if they honestly and practically rejoiced in God's glory. True love, then, sees this telos (everyone glorifying God) and moves people, things, and relationships towards it.
My Calculus II awaits. Let's see if I can do it to bring glory to God; instead of God loving me because I did it in a way that was pleasing. See the difference? I hope so. I think some of my pride comes from the old belief of God loving me because I accepted the sacrifice of His Son (this is true, but not the very bottom line). God created and saved men for His glory.