8 If, however, any one considers himself able, and has confidence enough, to give a clearer and better exposition of the question before us, God forbid that I should not be still more ready to learn than to teach. Only let no one dare to defend the freedom of the will in any such way as to attempt depriving us of the prayer that says, “Lead us not into temptation;” and, on the other hand, let no one deny the freedom of the will, and so venture to find an excuse for sin.
But let us give heed to the Lord, both in commanding and in offering His aid; in both telling us our duty, and assisting us to discharge it. For some He has let be lifted up to pride through an overweening trust in their own wills, while others He has let fall into carelessness through a contrary excess of distrust. The former say: Why do we ask God not to let us be overcome by temptation, when it is all in our own power? The latter say: Why should we try to live well, when the power to do so is in the hands of God?
O Lord, O Father, who art in heaven, lead us not into any of these temptations; but “deliver us from evil!” Listen to the Lord, when He says, “I have prayed for you, Peter, that your faith fail not;” that we may never think of our faith as so lying in our free will that it has no need of the divine assistance. Let us listen also to the evangelist, when he says, “He has given them power to become the sons of God;” that we may not imagine it as altogether beyond our own power that we believe: but in both let us acknowledge His beneficent acting.
For, on the one side, we have to give Him thanks that the power is bestowed; and on the other, to pray that our own little strength may not utterly fail. It is this very faith that works by love, according to the measure thereof that the Lord has given to every man; that he that glories may glory, not in himself, but in the Lord.
Source: Tractates on the Gospel of John (New Advent)