'Leaving father and mother' is leaving the internal man, for the internal is that which conceives and gives birth to the external. 'Clinging to his wife' is in order that the internal man may be within the external. 'Being one flesh' means that they are there together. Previously the internal man, and the external man deriving from the internal, were spirit, but now they have become flesh. In this way celestial and spiritual life was joined on to the proprium in order that they might seemingly be one.