You have heard that it was said by them of old time, You shall not commit adultery:
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Augustine of Hippo
AD 430
The lesser righteousness, therefore, is not to commit adultery by carnal connection; but the greater righteousness of the kingdom of God is not to commit adultery in the heart. Now, the man who does not commit adultery in the heart, much more easily guards against committing adultery in actual fact. Hence He who gave the later precept confirmed the earlier; for He came not to destroy the law, but to fulfil it.
Because adultery is a serious sin and in order to uproot it, lest our conscience be defiled, he forbade even lust, which is the fuel of adultery. According to the words of blessed James in his epistle, “Lust when it has conceived gives birth to sin; and sin when it is fullgrown brings forth death.” The Holy Spirit speaks concerning this to David: “Happy shall he be who takes your little ones and dashes them against the rock.” The symbolism here is that the blessed and truly evangelical person roots out the desires and lust of the flesh arising from human weakness. He does this immediately before they grow, at the onset, through faith in Christ who has been described as a rock. .
Ye have heard, &c. . . to lust after her—that Isaiah , with the design and object of indulging sinful passion with her—hath already committed adultery with her in his heart. Because by adultery he hath already corrupted her in his mind, and therefore before God, who beholds the heart, he is an adulterer, and as an adulterer he will be punished by Him.
Christ passes from anger to concupiscence, because these two passions have the greatest influence over men. And as He explained the commandment, Thou shall nor kill, to forbid anger, so He here explains Thou shall not commit adultery to forbid concupiscence. For many of the Scribes and Pharisees greatly erred in their exposition of this precept as well as of the former. For although they knew that it was commanded by the tenth precept of the Decalogue, Thou shall not covet thy neighbour"s wife, nevertheless they erred—1. Because they understood it of concupiscence, not altogether internal, but such as is wont to break out in touch, kisse...
For he did not simply say “whoever shall desire,” since it is possible for one to desire even when sitting alone in the mountains. Rather, Jesus said, “whoever looks with lust,” that is, one who thinks about another solely for the purpose of lusting, who, under no compulsion, allows the wild beast to intrude upon his thoughts when they are calm. This intrusion no longer comes from nature but from selfindulgence. The ancient Scripture corrects this from the first, saying, “Don’t gaze upon another’s beauty.” And then, so that no one should say, if I gaze but am not taken captive, he punishes the look, lest through a false security you should some time fall into sin. “What then,” one may say, “if I should look, and desire indeed, but do no evil?” Even so you find your place among the adulterers. For the Lawgiver has pronounced it, and you must not question further. For when you look once, twice or three times, you will perhaps have power to refrain; but if you make this your habitual prac...
Having now finished the former commandment, and having extended it unto the height of self-denial, He, advancing in course and order, proceeds accordingly unto the second, herein too obeying the law.
And yet, it may be said, this is not the second, but the third; for neither is the first, You shall not kill, but The Lord your God is one Lord.
Wherefore it is worth inquiring too, why He did not begin with that. Why was it then? Because, had He begun from thence, He must have enlarged it also, and have brought in Himself together with His Father. But it was not as yet time to teach any such thing about Himself.
And besides, He was for a while practising His moral doctrine only, being minded from this first, and from His miracles, to convince the hearers that He was the Son of God. Now, if He had said at once, before He had spoken or done anything, You have heard that it was said to them of old time, I am the Lord your God, and there is none other but me, but I say unto you, Wors...