From the pen of Dr. Reymond:
Romans 13:9ff: Before he turns to the specific problem of meat offered to idols, Paul brings to a conclusion his general section on ethics by quoting most of the second half of the Ten Commandments: ‘… he who loves his neighbor has fulfilled the law. For this, “You shall not commit adultery, You shall not murder, You shall not steal, You shall not covet,” and if there is any other commandment [and we may be sure that Paul knew that there were other commandments], it is summed up in this saying, “You shall love your neighbor as yourself.” Love does no wrong to a neighbor; love therefore is the fulfillment of the law.’ Paul indicates that the four commandments he mentions (the sixth, seventh, eighth, and tenth) do not comprise the whole law by adding the words, ‘and if there is any other commandment.’ And his appeal to the Decalogue in the way which he does, as that which the law of love fulfills, demonstrates the permanent and abiding relevance of the law. Paul’s specific appeal to the love obligation also reminds the Christian that his (Paul’s) standard is the same as Jesus had indicated in his summary of the Ten Commandments: ‘You shall love your neighbor as yourself’ (he quotes Lev 19:18 in Rom 13:9; see Mark 12:31; Matt 7:12). He correlates ‘love’ and ‘law’ by saying in 13:10 that ‘love is the fulfillment of the law’. Paul says again here then that the standard of ethics is the law. The very way in which it may be carried out or fulfilled is by the attitude and action of love. As Paul says in Galatians 5:6, 13, it is out of the Christian’s ‘new life’ in Christ that faith works through love. In sum, the norm or standard of the Christian life is the law, and the motive power to keep it is the new life in Christ, that is, life in the Spirit, which exhibits itself as a life of obedience which is the expression of love.
Love finds its direction and its parameters in the law of God. Love is not contentless or only a warm and undefined feeling, nor is it something that may be set in opposition to the law. The law does not need to be a ‘dead letter’, but neither is it an entity which has its own inherent strength. Love expresses the true intent and direction of the law as God’s good for man and as the way in which men properly express their love to God and man in the ethical realm.*
*Reymond, R. L. (2000). Paul, Missionary Theologian (476–477). Scotland: Christian Focus Publications.