Even a soul with an unsurpassable rank, such as that found within a complete tzaddik, is still not perfectly and totally unified with the divine being.
Even at its peak of love and fear of God, the soul remains an independent entity, one that experiences love toward another.
In this case, the object of this persons love is God.
Hence, there remain two distinct entities: the lover and the beloved.
Even when the soul reaches its ultimate purified state, it merits only to be close to God, yearning and aspiring toward the Divine, but never fully nullified to or unified with God.
Rabbi Adin Steinsaltz