What does it mean that "the two shall become one flesh" (Genesis 2:24)?

Being "one flesh" would indicate oneness of activity and purpose and also the physical relationship.

Marriage is the God-given relationship for the display of our natural affections and desires.

But again it is added, "So ought men to love their wives as their own bodies. He that loveth his wife loveth himself. For no man ever yet hated his own flesh; but nourisheth and cherisheth it, even as the Lord the church: for we are members of His body, of His flesh, and of His bones. For this cause shall a man leave his father and mother, and shall be joined unto his wife, and they two shall be one flesh. This is a great mystery: but I speak concerning Christ and the Church. Nevertheless let every one of you in particular so love his wife even as himself." (Eph. 5:28-33.) Here we are carried back, as has been remarked, to the garden of Eden, to the creation and presentation of Eve to Adam, which in itself is a manifest figure of the union between Christ and the church; and this fact accounts for the way in which the apostle weaves the two things in these exhortations. (See Gen. 2:21-25.) The union is thus looked upon as so complete — as Adam said of Eve, "This is now bone of my bones, and flesh of my flesh;" and again, "They shall be one flesh" — that it is said, so ought men to love their wives as their own bodies. In this aspect, self-love is to be the measure of a man's love to his wife; and as this is one of the instincts of our nature — and naturally its governing principle — it is impossible to conceive of a more definite and comprehensive direction. Let therefore the oneness of the union — they two shall be one flesh — be apprehended, and love will follow; for the husband will then no more consider his wife as distinct from, but as a part of himself. Thus whatever touches her, will touch him; and his self-love, moving now in a wider circle, includes her, and all that affects and concerns her, within its embrace. All that he desires for himself he will also desire for his wife; all the care he exercises for himself he will exercise for her; and all that he receives he will receive for her as well as for himself. In a word, all the good he seeks and all the evil he deprecates, he will also seek and deprecate for his wife, as for himself; for together they are "one flesh," and therefore he that loveth his wife loveth himself. The word of God provides in this way a perfect antidote against selfishness, and leads out the husband in self-sacrifice, which is the fruit of all true love, and which finds its highest exemplification in Christ, who loved the Church, and gave Himself for it.

Verse 24 puts on record the thought of God as to marriage from the outset, and to this the Lord Jesus appealed when answering the Pharisees, as recorded in Matthew 19:3-9. Deviation from this Divine thought and order, or worse still the denial of it, has probably been the cause of more sin and misery in the world than any other single fount of iniquity. When maturity is reached, a man is to leave father and mother and to found a new family, adhering to one woman as his wife. Thus they become one flesh. As we have just seen, Adam and Eve were one flesh to start with, since she was taken out of him.

Up to the time of a man's marriage the chief relationship in which he stands is that of a son, and his responsibility is towards his parents, but when he marries he leaves his father and mother and cleaves to his wife. Henceforward she becomes his chief care, for he and she are no more twain but one flesh.

Every right-minded man will look upon his wife as the only woman in the world for him, he will desire no other; and that not because he has chosen her for his wife, but because God has joined them together. He will look upon her as the very woman that God made for him; he will treat her as God's gift to him, and more, he will treat her as himself, for they twain have become one flesh; and that by no mere ordinance of man, but by God's own act and decree, hence "what God has joined together let not man put asunder."

Up to the time of a man's marriage the chief relationship in which he stands is that of a son, and his responsibility is towards his parents, but when he marries he leaves his father and mother and cleaves to his wife. Henceforward she becomes his chief care, for he and she are no more twain but one flesh.

Every right-minded man will look upon his wife as the only woman in the world for him, he will desire no other; and that not because he has chosen her for his wife, but because God has joined them together. He will look upon her as the very woman that God made for him; he will treat her as God's gift to him, and more, he will treat her as himself, for they twain have become one flesh; and that by no mere ordinance of man, but by God's own act and decree, hence “what God hath joined together let not man put asunder.”

But the Lord makes it transparently clear that the basic, original order in creation is not to be changed, but affirmed by the truth of the kingdom of heaven. God, in creating both male and female, made a marked distinction between them, but in marriage indicated a unity of vital character. Because of God's manifest order in creation it was right that a man should leave his father and mother and cleave to his wife. This verse settles many questions. First, when marriage takes place, the man (or woman) is no longer in the place of subjection to parents. Secondly, he cleaves to his wife:--only one wife, so that bigamy and polygamy are absolutely unscriptural. Cleaving to his wife involves genuine love for her, and faithfulness and devotedness.

The two are then recognized before God as being "one flesh." It is God Himself who has joined the two together. Therefore man has no authority to divorce them. Governments today of course ignore God's decree in this matter, but the word of God will not change to accommodate men's preferences. Marriage was from the beginning intended to be a binding agreement so long as both individuals remain alive.

As well as God's seeking to impress on us the reality of the relationship of Christ and the church, however, He is showing how close is the unity of husband and wife in God's sacred ordinance of marriage. Today this has been terribly violated by the selfish independence of both men and women, but God's word is plain, "For this cause a man shall leave his father and his mother, and shall cleave to his wife, and they shall become one flesh" (v.24). Thus God established marriage as the first of human relationships, and He makes it clear for all succeeding generations that a man should leave his father and mother and cleave to his wife. It is just as evident that the woman should leave her parents to become fully devoted to her husbands. The word "cleave" is beautiful here. It involves the reality of love, of devotedness and of faithfulness.

As well as God's seeking to impress on us the reality of the relationship of Christ and the church, however, He is showing how close is the unity of husband and wife in God's sacred ordinance of marriage. Today this has been terribly violated by the selfish independence of both men and women, but God's word is plain, “For this cause a man shall leave his father and his mother, and shall cleave to his wife, and they shall become one flesh” (v. 24). Thus God established marriage as the first of human relationships, and He makes if clear for all succeeding generations that a man should leave his father and mother and cling to his wife. It is just as evident that the woman should leave her parents to become fully devoted to her husband. The word “cling” is beautiful here. It involves the reality of love, of devotedness and of faithfulness.

The relationship established brings with it the joys and privileges peculiar to it, "They two shall be one flesh,"-joined in a unity such as no other relationship could possibly exhibit. It is theirs now to share in common the experiences and exercises of live, and what will also be welcome to the honourable heart, the responsibilities that have been willingly assumed by acceptance of one another. In all the experiences of life henceforth, let us firmly purpose to act consistently with this noble and blessed relationship. Let us not however expect in this a perfect state, for if so we shall be rightly disappointed. Indeed, it will be rather a further field of training in view of the perfect state, and it will be well if we gird ourselves to learn well by experiences of joy and sorrow, quietness and turmoil, rest and labour, distress and relief, pain and pleasure.

The primitive marriage in Eden was remarkably simple and exclusive. Two only shared the delights of the occasion. And this mutual reserve is a character marriage still retains. In matrimony two hearts, two lives become one exclusively in each other. At every wedding a new little world is formed with a total population of two numerically, but administratively of one only. How happy the new experience, and how momentous!