Matthew 19:5 Meaning

3The Pharisees also came unto him, tempting him, and saying unto him, Is it lawful for a man to put away his wife for every cause?

4And he answered and said unto them, Have ye not read, that he which made them at the beginning made them male and female,

5And said, For this cause shall a man leave father and mother, and shall cleave to his wife: and they twain shall be one flesh?

6Wherefore they are no more twain, but one flesh. What therefore God hath joined together, let not man put asunder.

7They say unto him, Why did Moses then command to give a writing of divorcement, and to put her away?