The Righteous, through their study of wisdom and through good deeds, cause Supernal Union between the Cosmic Man, called Zeir Anpin (Small Face) and the Cosmic Woman, called Nukva (Female). The union produces rejoicing in the spiritual worlds and leads to the creation of souls. Was this union possible before the Torah, specifically, in the days of Abraham, Isaac, and Jacob?
Unlike spiritual entities which never change, such as Truth, Beauty, and Righteousness, the Supernal Man undergoes transformations. Until the time of Abraham, his body was fully developed, but not his mind. Since the cause of the Union is the Mind, the Union could not take place.
That is why God told Abraham, “Lech-Lecha” - go to the Land of Israel, the land of Love, where you will arouse Love for the purpose of the Union. “...And I will make you into a great person...” speaks about the Cosmic Man, who will acquire the three mental capacities: Wisdom, Understanding, and Knowledge.
The name of Abraham is a hint that the Union started in his days. The letters A, B, R of Abraham form “Ever”, or the member. The letter M at the end of the word, which looks like a closed circle, hints at the connection between the Foundation (Ever) and the Female, represented by the closed letter Mem.