A better way

Disclaimer: I didn't plan this I just started writing, I'll probably edit it later.

This is the most logical argument I can think of. Being a Christian won't make your life easy, or happy, or rich or satisfied. What it will do is make it better than it would have been without Jesus.
Happiness seems to be the goal for so many people. I try to think of something comparable to this, it's sort of like always wanting to be laughing, or be angry. Happiness is an emotion, and no emotion is always sustainable, or appropriate for that matter. I think what people mean when they say "happy" is content. Contentedness is not emotional. It is logical, and it is a choice, like love. (infatuation and attraction are emotional, true Love is a choice.) It is looking at whatever situation you are in and saying, "I can live with this." or, short of that, saying, "I cannot live like this, therefore I will do something to change these circumstances or my attitude so that I can."
Real Contentedness, like real Love, is not possible without Jesus. All the logic in Vulcan cannot explain some of the awful things in life. Sometimes it takes Jesus saying, "this is the best way" before we do something. and in hindsight it does turn out to be the best way. In true hindsight, when we are all dead, we will see our lives and say, "shoot, that would have been better." because none of us does what is right all the time.