Matthew 19:4

‘And he answered and said, “Have you not read, that he who made them from the beginning made them male and female,

‘Have you not read?' Jesus then turned their attention to what the Scriptures did say, and that was that God had made man ‘male and female'. The two were to be seen as one. Genesis 1:27 says, ‘God created man in His own image, in the image of God He created him, male and female He created them.' In other words God's image was reflected and revealed among other ways (e.g. their spiritual nature) in the oneness of the male and female. A man was thus incomplete without his female counterpart, and once they were joined together they were reunited as one. This was the basis and purpose of the creation of mankind.

‘From the beginning.' That is, from Genesis 1:1 and what followed. There was never a time when it was not so, however primitive man was. Marriage was always intended to be monogamous and permanently binding, and had been from the beginning.