Now the Lord Himself not only shows us what evil we should shun, and what good we should do, which is all that the letter of the law is able to effect; but He moreover helps us that we may shun evil and do good, which none can do without the Spirit of grace; and if this be wanting, the law comes in merely to make us guilty and to slay us.—St. Augustine, On Rebuke and Grace
Bellarmine (De Rom. pontific., bk. 3, ch. 23, antith. 6): “We are not afraid to assert that a man, justified by the grace of God, can by the aid of the same grace both fulfill the Law and by that fulfillment merit eternal life.”