Gay marriage is forbidden.
Mt 5:17
"Do not think that I came to abolish the Law or the Prophets; I did not come to abolish but to fulfill. 18
For truly I say to you, until heaven and earth pass away, not the smallest letter or stroke shall pass from the Law until all is accomplished.
The best interpretation of these difficult verses says that Jesus fulfills the Law and the Prophets in that they point to him, and he is their fulfillment. The antithesis is not between "abolish" and "keep" but between "abolish" and "fulfill." "For Matthew, then, it is not the question of Jesus 'relation to the law that is in doubt but rather its relation to him!" (Robert Banks, "Matthew's Understanding of the Law: Authenticity and Interpretation in Matthew 5:17- 20," JBL 93 [1974]:226- 42).
Three theological conclusions are inevitable.
1. If the antitheses (vv. 21- 48) are understood in the light of this interpretation of vv. 17- 20, then Jesus is not primarily engaged there in extending, annulling, or intensifying OT law, but in showing the direction in which it points, on the basis of his own authority (to which, again, the OT points). This may work out in any particular case to have the same practical effect as "intensifying" the law or "annulling" some element; but the reasons for that conclusion are quite different. On the ethical implications of this interpretation, see the competent essay by Moo ("Jesus").
2. If vv. 17- 20 are essentially authentic (see esp. W. D. Davies, "Matthew 5:17, 18," Christian Origins and Judaism [London

LT, 1962], pp. 31- 66; and Banks, "Matthew's Understanding") and the above interpretation is sound, the christological implications are important. Here Jesus presents himself as the eschatological goal of the OT, and thereby its sole authoritative interpreter, the one through whom alone the OT finds its valid continuity and significance.
3. This approach eliminates the need to pit Matthew against Paul, or Palestinian Jewish Christians against Pauline Gentile believers, the first lot adhering to Mosaic stipulations and the second abandoning them. Nor do we need the solution of Brice Martin, who argues that Matthew's approach to law and Paul's approach are non complementary but noncontradictory: they simply employ different categories. This fails to wrestle with Matthew's positioning of Jesus within the history of redemption; and Paul well understood that the Law and the Prophets pointed beyond them selves (e. g., Rom 3:21; Gal 3:4; cf. Rom 8:4). The focus returns to Jesus, which is where, on the face of it, both Paul and Matthew intend it to be. The groundwork is laid out in the Gospels for an understanding of Jesus as the one who established the essentially christological and eschatological approach to the OT employed by Paul. But this is made clearer in v. 18.
Mt 15:19
For out of the heart come evil thoughts, murders, adulteries, fornications, thefts, false witness, slanders. 20
These are the things which defile the man.
17- 20 Verse 17 explains that "what goes into a man's mouth" (v. 11) is merely food, which passes through the body and is excreted (lit., "is cast into a latrine"). On the sanitary conditions of the time, cf. Edward Neufeld, "Hygiene Conditions in Ancient Israel," Biblical Archaeologist 34 (1971):42- 66. Verses 18- 20 explain that "what comes out of a man's mouth" (v. 11), and what makes him unclean, comes from his heart (see on 12:34- 35). Matthew's list of the heart's products (v. 19) is shorter than Mark's. After the first, "evil thoughts," the list follows the same order as the sixth and seventh commandments, followed by porneia ("sexual immorality"; see on 19:3- 12), the order of the eighth and ninth commandments, and finally "slander," which probably includes blasphemy (cf. 12:31). The list itself negates (as Banks [Jesus, pp. 143- 44] points out) Kilpatrick's suggestion that Matthew has transformed Mark's principle of morals into a precept of law (Origins, p. 38).
It would be puerile to ask how every item on the list results directly in defiling speech. The point, as in 12:34- 35, is that what a man truly is affects what he says and does. Jesus presupposes that the heart is essentially evil (cf. 7:11). But the burden of this pericope is not to be pure on the inside and forget the externals but that what ultimately defiles a man is what he really is. Jesus is not spiritualizing the OT but insisting that true religion must deal with the nature of man and not with mere externals.
Mt 19:4b
"Have you not read that He who created them from the beginning made them male and female, 5
and said, ' For this reason A man shall leave his father and mother and be joined to his wife, and the two shall become one flesh '? 6
So they are no longer two, but one flesh. What therefore God has joined together, let no man separate."
Note 4- 6 Jesus aligns himself with the prophet Malachi, who quotes Yahweh as saving, "I hate divorce" (2:16), and also refers to creation (2:14- 15). Jesus cites first Genesis 1:27 and then Genesis 2:24. The Creator made the race "male and female" (v. 4):the implication is that the two sexes should be united in marriage. But lest the implication be missed, the Creator then said that "for this reason" (v. 5)-- because God made them so-- a man will leave father and mother, be united to his wife, and become one flesh (cf. Ecclesiasticus 25:26; Eph 5:28- 31).
The words "for this reason" in Genesis 2:24 refer to Adam's perception that the woman was "bone of his bone and flesh of his flesh" because she had been made from him and for him-- i. e., the man and the woman were in the deepest sense "related." The same thing is implied by Genesis 1:27-- i. e., the "one flesh" in every marriage between a man and a woman is a reenactment of and testimony to the very structure of humanity as God created it.
"So" (hoste here is "simply an inferential particle" [Moule, Idiom Book, p. 144]), Jesus concludes, the husband and wife are no longer two but one, and that by God's doing (v. 6). If God has joined them together, according to the structure of his own creation, divorce is not only "unnatural" but rebellion against God. God and man are so far apart on this issue that what God unites, man divides.
Jesus 'response cuts through a great deal of casuistry and sets forth a dominant perspective that must not be lost in the exegetical tangles of v. 9. Two profound insights must be grasped.
1. Although Jewish leaders tended to analyze adultery in terms, not of infidelity to one's spouse, but of taking someone else's wife (cf. M Ketuboth and M Kiddushin), Jesus dealt with the sanctity of marriage by focusing on the God- ordained unity of the couple.
2. Jesus essentially appealed to the principle, "The more original, the weightier," an accepted form of argument in Jewish exegesis (cf. Paul in Gal 3:15- 18); and it is impossible to go further back than creation for the responsibilities of mankind. If marriage is grounded in creation, in the way God has made us, then it cannot be reduced to a merely covenantal relationship that breaks down when the covenantal promises are broken (contra David Atkinson, To Have and to Hold:The Marriage Covenant and the Discipline of Divorce [London:Collins, 1979], esp. pp. 114ff.). But the argument in this instance leaves unanswered the question of how the Mosaic law is to be taken; and therefore the stage is set for the Pharisees' next question.