Though the answer wouldn’t be obvious to unbelievers or even to most Christians, the Bible is clear on this: it’s Jesus. 

It’s not the people who know God who have reason to be miserable—it’s those who don’t. Unfortunately, children who grow up seeing church as a morose, hypercritical place will turn their backs on it in their quest for happiness. Those who have found happiness in the church, and ultimately in Christ, will usually stay or return.

My wife led a women’s Bible study group in discussing a lesson she’d written about the happiness of Jesus. One woman who’d grown up as a churchgoer was startled. She shared how horrified she’d once been to see a picture of Jesus smiling. Why? Because she believed it was blasphemous to make Jesus appear happy!