Owe no man anything
From the payment of dues to magistrates the apostle proceeds to a general exhortation to discharge all sorts of debts; as not to owe the civil magistrate any thing, but render to him his dues, so to owe nothing to any other man, but make good all obligations whatever, as of a civil, so of a natural kind. There are debts arising from the natural and civil relations subsisting among men, which should be discharged; as of the husband to the wife, the wife to the husband; parents to their children, children to their parents; masters to their servants, servants to their masters; one brother, friend, and neighbour, to another. Moreover, pecuniary debts may be here intended, such as are come into by borrowing, buying, commerce, and contracts; which though they cannot be avoided in carrying on worldly business, yet men ought to make conscience of paying them as soon as they are able: many an honest man may be in debt, and by one providence or another be disabled from payment, which is a grief of mind to him; but for men industriously to run into debt, and take no care to pay, but live upon the property and substance of others, is scandalous to them as men, and greatly unbecoming professors of religion, and brings great reproach upon the Gospel of Christ.
But to love one another.
This is the only debt never to be wholly discharged; for though it should be always paying, yet ought always to be looked upon as owing. Saints ought to love one another as such; to this they are obliged by the new commandment of Christ, by the love of God, and Christ unto them, by the relations they stand in to one another, as the children of God, brethren, and members of the same body; and which is necessary to keep them and the churches of Christ together, it being the bond of perfectness by which they are knit to one another; and for their comfort and honour, as well as to show the truth and reality of their profession. This debt should be always paying; saints should be continually serving one another in love, praying for each other, bearing one another's burdens, forbearing each other, and doing all good offices in things temporal and spiritual that lie in their power, and yet always owing; the obligation to it always remains. Christ's commandment is a new one, always new, and will never be antiquated; his and his Father's love always continue, and the relations believers stand in to each other are ever the same; and therefore love will be always paying, and always owing in heaven to all eternity. But what the apostle seems chiefly to respect, is love to one another as men, love to one another, to the neighbour, as the following verses show. Love is a debt we owe to every man, as a man, being all made of one blood, and in the image of God; so that not only such as are of the same family, live in the same neighbourhood, and belong to the same nation, but even all the individuals of mankind, yea, our very enemies are to share in our love; and as we have an opportunity and ability, are to show it by doing them good.
For he that loveth another hath fulfilled the law;
that is, not who loves some one particular person, but every other person besides himself, even his neighbour, in the largest sense of the word, including all mankind, and that as himself; such an one has fulfilled the law, the law of the decalogue; that part of it particularly which relates to the neighbour; the second table of the law, as the next verse shows: though since there is no true love of our neighbour without the love of God, nor no true love of God without the love of our neighbour; and since these two involve each other, and include the whole law, it may be understood of fulfilling every part of it, that is, of doing it; for fulfilling the law means doing it, or acting according to it; and so far as a man loves, so far he fulfils, that is, does it: but this is not, nor can it be done perfectly, which is evident, partly from the impotency of man, who is weak and without strength, yea, dead in sin, and unable to do any thing of himself; and partly from the extensiveness of the law, which reaches to the thoughts and desires of the heart, as well as to words and actions; as also from the imperfection of love, for neither love to God, nor love to one another, either as men or Christians, is perfect; and consequently the fulfilling of the law by it is not perfect: hence this passage yields nothing in favour of the doctrine of justification by works; since the best works are imperfect, even those that spring from love, for love itself is imperfect; and are not done as they are, in a man's own strength, and without the Spirit and grace of God. Christ only has fulfilled the law perfectly, both as to parts and degrees; and to him only should we look for a justifying righteousness.