What God promises, we ourselves do not through free will of human nature, but He Himself does by grace within us - Augustine

"If, therefore, they are servants of sin (II Cor. 3:17), why do they boast of free will? … O, man! Learn from the precept what you ought to do; learn from correction, that it is your own fault you have not the power … Let human effort, which perished by Adam, here be silent, and let the grace of God reign by Jesus Christ … What God promises, we ourselves do not through free will of human nature, but He Himself does by grace within us … Men labour to find in our own will something that is our own, and not God’s; how can they find it, I know not."

- Augustine