 For by grace you say through faith and that not of yourselves, it is the gift of God, not of works, lest any man should boast. See where it says that not of yourselves? That is further defined, that is further explained in the next verse where it says not of works. It's not of yourselves, therefore the best you can offer is your works and it's not of works because it's not of you. You're not saved of yourself, you're saved by what Christ did for you. You put your faith in him that he made the payment for your sins so you don't have to.