Faith Completes What the Law Cannot Achieve

[Paul] neither extols the Law unduly, owing to Jews' impudence, nor does he provide the impious heretics with an occasion of criticism.  Instead he shows it giving the necessary instruction and proposing the teaching of righteousness, though unable to achieve this on account of the weakness of those on whom the law was imposed.  Then he teaches that faith put into effect the aim of the Law: what the latter was willing but unable to achieve, faith brought to completion through the grace of the all-holy Spirit.

Theodoret of Cyrus, "The Letter to the Romans"*

* Commentary on the Letters of St. Paul, Vol 1, (trans. Robert C. Hill; Brookline, MA: Holy Cross Orthodox, 2001), 43.