Augustine of Hippo, On Rebuke and Grace Chapter 3: What the Grace of God Through Jesus Christ is

For the grace of God through Jesus Christ our Lord must be apprehended,—as that by which alone men are delivered from evil, and without which they do absolutely no good thing, whether in thought, or will and affection, or in action; not only in order that they may know, by the manifestation of that grace, what should be done, but moreover in order that, by its enabling, they may do with love what they know. Certainly the apostle asked for this inspiration of good will and work on behalf of those to whom he said, “Now we pray to God that ye do no evil, not that we should appear approved, but that ye should do that which is good.” Who can hear this and not awake and confess that we have it from the Lord God that we turn aside from evil and do good?—since the apostle indeed says not, We admonish, we teach, we exhort, we rebuke; but he says, “We pray to God that ye do no evil, but that ye should do that which is good.” And yet he was also in the habit of speaking to them, and doing all those things which I have mentioned,—he admonished, he taught, he exhorted, he rebuked. But he knew that all these things which he was doing in the way of planting and watering openly were of no avail unless He who giveth the increase in secret should give heed to his prayer on their behalf. Because, as the same teacher of the Gentiles says, “Neither is he that planteth anything, neither he that watereth, but God that giveth the increase.”