The Cause of Joy is Jesus

One of the things that mark the Christmas is joy. In Luke about the birth of Christ we read: "Do not be afraid. I bring you good news that will cause great joy for all the people.' And we see at the end of Jesus' life he says these words: "I am coming to you now, but I say these things while I am still in the world, so that they may have the full measure of my joy within them." Jesus' grace is what brings joy and thankfulness to us. Why did it take so long to fully understand God's grace. Was it the Holy Spirit that revealed this to me? Clay calls about Luke 2 concerning census and taxation. Jesus has already forgiven past present and future sins so shouldn't we just confess our sin instead of asking forgiveness?