III.—OF LOVE AND THE FULFILMENT OF THE LAW. On this point our opponents meet us with the declarations, Matt. 19:17 : “if thou wilt enter into life, keep the commandments ;” and Rom. 2:13 : “Not the hearers of the law are just before God, but the doers of the law shall be justified ;” besides many similar passages, relative to the law and to works. Before we reply to this, it is necessary for us to state our views concerning love and the fulfilment of the law.
It is written in the Prophet Jer. 31:33 : “I will put my law in their inward parts ;” and Rom. 3:31, Paul says : “Do we then make void the law through faith ? God forbid : yea, we establish the law.” Again, Christ says, Matt. 19:17 : “If thou wilt enter into life, keep the commandments.” Paul also says to the Corinthians, 1 Cor. 13:3 : “If I have not charity, it profiteth me nothing.” These and similar passages show that we must keep the law, when we are justified by faith, and thus increase more and more in the Spirit. We are not, however speaking of the Mosaic ceremonies, but the Ten Commandments, which require us to fear and love God truly, from the bottom of our hearts. Now, since faith is accompanied by the Holy Spirit, and produces in the heart a new light and life, it is true, and necessarily follows, that faith renews and changes the heart. What kind of a renovation of the heart this is, we learn from the Prophet, when he says : “I will put my law in their inward parts.”
Accordingly, when we are born anew by faith, and know, that God will be merciful to us, and be our father and our helper, we begin to fear, love, thank, and praise him, to entreat and look to him for assistance, and to submit to his will in afflictions ; then we also being to love our neighbor. Then there is, within us a new heart, mind, and soul, through the Spirit of Christ.
(Henkel Translation, p. 180).