Augustine of Hippo

Therefore, God commands continence, and he gives continence; he commands by the law, he gives by the Spirit; for the law without grace makes sin abound, and the letter without the spirit kills. He commands so as to make us learn how to ask the help of grace when we try to obey his commandments and in our weakness fall wearied under the law, and also to make us grateful to him who helps us if we have been able to perform any good work.