The mystery of Coupling depends on the reign of unity so that the vessels of Zeir Anpin and the Nukva actually become attached in such a way as to be considered literally one – just like the interior, which is already one. This is the meaning of the verse, “And they shall become one flesh” (Genesis 2:24). It begins with Kissing, which is the joining together of the Ruach – i.e. the interior, which becomes so powerfully unified that it even causes the exteriors to become attached to one another.
However this comes about only when both Zeir Anpin and Nukva are complete. Zeir Anpin must be complete with all his Mental Powers and all the higher Partzufim bound to him to adorn him. Nukva must be complete with all the repairs she receives through the lower creations, which are bound up with her. The completeness of the preparations determines the completeness of the Coupling, which may be through the mystery of Israel and Rachel or through their other branches, male and female.