1 And that the Lord did not abrogate the natural [precepts] of the law, by which man is justified, which also those who were justified by faith, and who pleased God, did observe previous to the giving of the law, but that He extended and fulfilled them, is shown from His words. “For,” He remarks, “it has been said to them of old time, Do not commit adultery. But I say unto you, That every one who has looked upon a woman to lust after her, has committed adultery with her already in his heart.” And again: “It has been said, You shall not kill. But I say unto you, Every one who is angry with his brother without a cause, shall be in danger of the judgment.” And, “It has been said, You shall not forswear yourself. But I say unto you, Swear not at all; but let your conversation be, Yea, yea, and Nay, nay.” And other statements of a like nature. For all these do not contain or imply an opposition to and an overturning of the [precepts] of the past, as Marcion's followers do strenuously maintain; but [they exhibit] a fulfilling and an extension of them, as He does Himself declare: “Unless your righteousness shall exceed that of the scribes and Pharisees, you shall not enter into the kingdom of heaven.” For what meant the excess referred to? In the first place, [we must] believe not only in the Father, but also in His Son now revealed; for He it is who leads man into fellowship and unity with God. In the next place, [we must] not only say, but we must do; for they said, but did not. And [we must] not only abstain from evil deeds, but even from the desires after them. Now He did not teach us these things as being opposed to the law, but as fulfilling the law, and implanting in us the varied righteousness of the law. That would have been contrary to the law, if He had commanded His disciples to do anything which the law had prohibited. But this which He did command— namely, not only to abstain from things forbidden by the law, but even from longing after them— is not contrary to [the law], as I have remarked, neither is it the utterance of one destroying the law, but of one fulfilling, extending, and affording greater scope to it.
2. For the law, since it was laid down for those in bondage, used to instruct the soul by means of those corporeal objects which were of an external nature, drawing it, as by a bond, to obey its commandments, that man might learn to serve God. But the Word set free the soul, and taught that through it the body should be willingly purified. Which having been accomplished, it followed as of course, that the bonds of slavery should be removed, to which man had now become accustomed, and that he should follow God without fetters: moreover, that the laws of liberty should be extended, and subjection to the king increased, so that no one who is converted should appear unworthy to Him who set him free, but that the piety and obedience due to the Master of the household should be equally rendered both by servants and children; while the children possess greater confidence [than the servants], inasmuch as the working of liberty is greater and more glorious than that obedience which is rendered in [a state of] slavery.
3. And for this reason did the Lord, instead of that [commandment], “You shall not commit adultery,” forbid even concupiscence; and instead of that which runs thus, “You shall not kill,” He prohibited anger; and instead of the law enjoining the giving of tithes, [He told us] to share all our possessions with the poor; and not to love our neighbours only, but even our enemies; and not merely to be liberal givers and bestowers, but even that we should present a gratuitous gift to those who take away our goods. For “to him that takes away your coat,” He says, “give to him your cloak also; and from him that takes away your goods, ask them not again; and as you would that men should do unto you, do unto them:” so that we may not grieve as those who are unwilling to be defrauded, but may rejoice as those who have given willingly, and as rather conferring a favour upon our neighbours than yielding to necessity. “And if any one,” He says, “shall compel you [to go] a mile, go with him two;” so that you may not follow him as a slave, but may as a free man go before him, showing yourself in all things kindly disposed and useful to your neighbour, not regarding their evil intentions, but performing your kind offices, assimilating yourself to the Father, “who makes His sun to rise upon the evil and the good, and sends rain upon the just and unjust.” Now all these [precepts], as I have already observed, were not [the injunctions] of one doing away with the law, but of one fulfilling, extending, and widening it among us; just as if one should say, that the more extensive operation of liberty implies that a more complete subjection and affection towards our Liberator had been implanted within us. For He did not set us free for this purpose, that we should depart from Him (no one, indeed, while placed out of reach of the Lord's benefits, has power to procure for himself the means of salvation), but that the more we receive His grace, the more we should love Him. Now the more we have loved Him, the more glory shall we receive from Him, when we are continually in the presence of the Father.
4. Inasmuch, then, as all natural precepts are common to us and to them (the Jews), they had in them indeed the beginning and origin; but in us they have received growth and completion. For to yield assent to God, and to follow His Word, and to love Him above all, and one's neighbour as one's self (now man is neighbour to man), and to abstain from every evil deed, and all other things of a like nature which are common to both [covenants], do reveal one and the same God. But this is our Lord, the Word of God, who in the first instance certainly drew slaves to God, but afterwards He set those free who were subject to Him, as He does Himself declare to His disciples: “I will not now call you servants, for the servant knows not what his lord does; but I have called you friends, for all things which I have heard from My Father I have made known.” For in that which He says, “I will not now call you servants,” He indicates in the most marked manner that it was Himself who did originally appoint for men that bondage with respect to God through the law, and then afterwards conferred upon them freedom. And in that He says, “For the servant knows not what his lord does,” He points out, by means of His own advent, the ignorance of a people in a servile condition. But when He terms His disciples “the friends of God,” He plainly declares Himself to be the Word of God, whom Abraham also followed voluntarily and under no compulsion (sine vinculis), because of the noble nature of his faith, and so became “the friend of God.” But the Word of God did not accept of the friendship of Abraham, as though He stood in need of it, for He was perfect from the beginning (“Before Abraham was,” He says, “I am”), but that He in His goodness might bestow eternal life upon Abraham himself, inasmuch as the friendship of God imparts immortality to those who embrace it.
Source: Adversus haereses (New Advent)