Mystery

Driving home today I witnessed the following bumper sticker on the back of a fading red car:

"If only life were as simple as evangelism."

I don't get it. I feel like I should understand it, but I'm really just confused by it. Is it sarcastic? Tounge-in-cheek? Serious? I really don't know what its intent is and I can't for the life of me figure out what it means.

Thoughts? Interpretations?