Every human being is a confederacy of parts as expressed most explicitly in the Hebrew word adam meaning "man," which can be divided into two fragments. The first is simply the letter aleph. It is the first symbol of the alphabet, has the numerical equivalent of 1 (which signifies oneness/unity), and is soundless in its pronunciation. As such, it is the most spiritual and rarified of letters, and always hints to the transcendent level of God. The second fragment of the word adam spells dam meaning "blood" and thus identifies the physical level of earthy body, of flesh and blood.
Human beings are unique among created things for exactly this reason. They fuse within themselves, albeit often precariously, the two poles of Divine reality: God's innermost, infinitely spiritual, and pure unity; and His outermost realms that seem to be defined by physicality and multiplicity. While as physical as the lowest of created entities, human beings have a soul that is an actual portion of God above.
Kabbalah refers to these two basic constituents of human beings as the Divine soul and the physical soul. They are almost mirror images of each other in terms of their "anatomy," with one slight variation, but that slight variation makes all the difference. At its highest and most sublime level, the Divine soul is directly and continuously connected with God. From that point of actual union, it extends down through the spiritual, mental, emotional and physical planes; but it always remains connected to God's Infinite Light (Or Ain Sof) from which it sprang. The physical soul also has these very same levels, but does not, in itself, possess a direct connection with God’s Infinite Light. It can only experience this ultimate level indirectly, via the Divine soul.
Both the physical soul and the Divine soul aspire toward unity but in proportion to their own capabilities and world views. The Divine soul seeks to dissolve itself in the Infinite Light of God. The physical soul, on the contrary, can’t really see beyond the outline of its own shadow, and so its definition of oneness is likewise limited. Therefore it strives for unity through physics and the unified field theory, telecommunications, universalism, sexuality, etc. But all those things, which unify the physical pole of reality but still preserve a level of individuality, by definition require a degree of separation from God. The leap into complete union is only possible to the extent that these endeavors are explicitly subsumed within a larger context of God's law.