In what way are churches failing to offer the happiness the world longs for?
The gospel of the Messiah's redemptive work is called "good news of happiness" (Isaiah 52:7, ESV), synonymous with what Luke calls "good news of great joy for all the people" (Luke 2:10, ISV). Unfortunately, I believe the modern church is often driven more by duty than by delight in God. The misguided distinction between joy and happiness has played a part in driving people away from the happiness the gospel offers. To declare joy sacred and happiness secular closes the door to dialogue with unbelievers. If someone is told that joy is the opposite of happiness, any thoughtful person would say, "In that case, I don't want joy!"
The word happiness has historically had a common meaning for both believers and unbelievers—and for many it still does. Until recent decades, it's been a bridge between the church and the world—one we can't afford to burn. If we say the gospel won't bring happiness, any perceptive listener should respond, "Then how is it good news?" We need to reverse the trend. Let's redeem the word happiness in light of both Scripture and church history. Our message shouldn't be "Don't seek happiness" but "You'll find in Jesus the happiness you've always longed for."
What do you want readers of your book to do once they finish it?
First, my hope is that readers will meditate on and embrace the scriptural teaching about God's happiness
Second, I hope readers will seek to cultivate a Christ-centered happiness that will affect every area of their lives and will spill over into the lives of their family, friends, and acquaintances. People are drawn to Christ when they see true happiness in his followers and are pushed away when they see us chronically unhappy. (Sure, we sometimes experience sorrow or battle depression, but rejoicing in God is still possible.)