Grace by Installment

If we are saved by grace alone, then why do most Christians live as if they are paying for their salvation by installments?

I think we need to realize that the result of both the evil and good of the Tree of Knowledge of Good and Evil is death. The good part is still as deadly as the evil. We need to partake of the fruit from the Tree of Life for us to truly live.

And we can only do so by grace. Meaning, it's undeserved. Nothing bad we did can disqualify us from it; nothing good we can ever accomplish can qualify for it either.

I guess it's about time we truly serve God and not just our guilty conscience.