It is good news that God is gloriously happy. No-one would want to spend eternity with an unhappy God. If God is unhappy, then the goal of the gospel is not a happy goal, and that means it would be no gospel at all. But, in fact, Jesus invites us to spend eternity with a happy God when he says, "Enter into the joy of your master" (Matthew 25:23). Jesus lived and died that his joy - God's joy - might be in us and our joy might be full (John 15:11; 17:13).
John Piper, The Pleasures of God, p.26