Keter of Zeir Anpin is the mystery of Arich Anpin. Just as Abba and Imma govern Zeir Anpin through his Mental Powers, so too Arich Anpin enters through the Keter of Zeir Anpin in order to direct Zeir Anpin to the ultimate goal of the revelation of the unity.
The entry of Abba and Imma into Zeir Anpin generates additional Partzufim: Jacob and Leah and the diagonals.