Thomas Aquinas

“ Although the grace of the New Testament helps man to avoid sin, yet it does not so confirm man in good that he cannot sin: for this belongs to the state of glory. Hence if a man sin after receiving the grace of the New Testament, he deserves greater punishment, as being ungrateful for greater benefits, and as not using the help given to him. And this is why the New Law is not said to "work wrath": because as far as it is concerned it gives man sufficient help to avoid sin. ”

“ Because the state of the New Law succeeded the state of the Old Law, as a more perfect law a less perfect one. Now no state of the present life can be more perfect that the state of the New Law: since nothing can approach nearer to the last end than that which is the immediate cause of our being brought to the last end. ”

“ The third reason is found in the fact that the New Law is the law of grace: wherefore it behoved man first of all to be left to himself under the state of the Old Law, so that through falling into sin, he might realize his weakness, and acknowledge his need of grace. ”