Mat 5:27 Ye have heard that it was said by them of old time, Thou shalt not commit adultery:
You have understood what was proclaimed, "You may not betray."
this is the second commandment that Christ discusses in this section. This may mean that it is the second most important moral issue in his commandments. He often describes the current generation as "adulterous" (Mat 12:39). The "you" here is plural, addressed to all the crowd.
The word translated here as "ye hath heard," is the most common verb that Christ uses meaning "to hear". It also means "to listen" and "to understand."
The verb translated as "it was said," however, is a very uncommon verb for Christ to use to refer to simply saying or speaking. There are three other Greek verbs that are much more commonly used to say "said" or "tell". This verb is a more serious meaning, "to proclaim" or "to pronounce," which better fits the context.
The phrase in the KJV "by the ancients," does not appear in today's better Greek sources. It is a duplication of a line in Mat 5:17, a verse that begins the same as this one. Most more modern translations have dropped it conforming to the oldest Greek manuscripts.
The Greek translated as "not" is the objective negative of facts, not the subjective negative of opinions. It is the negative used with prohibitions.
The most interesting word here, however, is the Greek verb translated as "shall commit adultery" means "to debauch a woman" that is, to degrade a person by having sex outside of marriage. The concept is used more broadly to mean degrading people in general, specifically by encouraging them to break their vows. However, in English, we use the term "betray" to capture this concept. This more general meaning is useful because "betray" is, like the Greek verb, transitive. You can "betray a woman" but you cannot "adultery a woman", which is how this word is used in the next verse, Mat 5:28. Christ also seems to use the concept "adulterous" more generally to refer to as a certain type of people (the meaning of the Greek word translated as "generation" in the Bible). He seems to a lack of faith, rather than actual sexual seduction (Mat 16:4). The word is also used to refer to idolatry. The woman in the next verse could be symbolic of idolatry. Christ sees idolatry as worshiping the pleasures of this world.
First, the form of the verb can be parsed to different ways. The KJV translation has it as the future, active. The form that indicates something that might happen is strongly indicated by the earlier verse that followed this form: Mat 5:17. There the verb was in the form of possibility as well and required because of the use of the Greek word "an," which indicates a possibility. The difference is using "may" instead of "shall," a statement of possibility rather than a statement of fact.
The sense here is that adultery is corrupting ("adulterating") activities violating vows to God. The central vow in human relationships is the marriage vow.
A play of the two meanings of adultery, sexual cheating and religious cheating.
The Spoken Version:
“My last penny went to wine,” complained a slightly drunken voice, getting a few hoots.
“My last penny went to my wife,” said another, winning an even larger laugh.
“My last penny went to some women who weren’t my wife,” said a third joker suggestively. This won the biggest laugh of all but many groans.
The speaker was smiling, but he was also shaking his head, no.
“You have heard that it has been said—,” he repeated. Then again, switching to his old man’s voice, he pretended to read from a scroll, “‘You don’t want to betray your vows!’”
Ἠκούσατε (2nd pl aor ind act) "Ye have heard" is from akouo, which means "hear of", "hear tell of", "what one actually hears", "know by hearsay", "listen to", "give ear to", "hear and understand," and "understand."
ὅτι (conj) "That" is from hoti, which introduces a statement of fact "with regard to the fact that", "seeing that," and acts as a causal adverb meaning "for what", "because", "since," and "wherefore."
ἐρρέθη (3rd sg aor ind pass) "It was said" is from ero, which means "to say", "to speak", ""to proclaim", "to announce", "to tell", "to order," "to be pronounced [passive]", "to let suffice [passive]", "to have been given orders", "to be mentioned," and "to be specified, agreed, or promised."
“Οὐ (partic) "Not" is from ou which is the negative adverb for facts and statements, negating both single words and sentences. The other negative adverb, μή applies to will and thought; οὐ denies, μή rejects; οὐ is absolute, μή relative; οὐ objective, μή subjective.
μοιχεύσεις.” (2nd sg aor subj act or 2nd sg fut ind act) "Commit adultery" is from moicheuo, which means "commit adultery with a woman, " "to debauch a woman," and generally, "to commit adultery with anyone." It is a metaphor for "worshiping idolatrously."