Jeez, you guys . . . are you maybe reading in just a little much?
One of the basic tenets of Christianity is that nobody can measure up to the “demands” of God. No human, that is. We’re also incapable of earning our own forgiveness for our failure to measure up (and some say we’re incapable even of *desiring * our own forgiveness, but that’s a whole 'nother issue).
The bumper sticker is intended to be humorous, and, yes, humble. Christians aren’t perfect, not even close, and they’re the first ones to admit it. They’ve already been convicted of frailty and failure by the teachings of their faith. But they’re constantly amazed and thankful that they’ve been forgiven . . . over and over and over again. As often as they ask for it.
It doesn’t say “God says you suck” - it doesn’t say anything about **you ** at all (sorry, not *everything’s * about you after all).
The idea that Christians don’t get to boast - I’m not sure where this comes from. Certainly not from the Christians themselves. Paul is boasting all over the place in the New Testament - “look at me! I’ve been forgiven even though I’m not worthy!” “Hey look! God stooped down to consider me, even though I’m a flawed vessel” (paraphrasing from memory, folks, don’t ask for chapter and verse on these two specific quotes). The “boasting” and “arrogance” you guys seem to find in this bumper sticker are of the same nature - “I’m a fuck-up, but God loves me anyhow; woo-hoo!”