Da'at is the third and last conscious power of intellect in Creation.
Generally, da'at is only enumerated among the sefirot when keter is not. This is due to the fact that da'at represents the reflection of (the inner dimension of) keter itself within the realm of consciousness (as described above). Hence da'at appears in the configuration of the sefirot along the middle axis, directly beneath keter; and, corresponds in the tzelem Elokim to the cerebellum (posterior brain).
Da'at is associated in the soul with the powers of memory and concentration, powers which rely upon one's "recognition" (hakarah) of, and "sensitivity" (hergesh) to, the potential meaningfulness of those ideas generated in consciousness through the powers of chochmah and binah. This sensitivity itself derives from da'at's connection to the superconscious origin of the soul.
In general, da'at operates on two levels: the higher level, referred to as da'at elyon ("higher knowledge") or da'at hane'elam ("the hidden knowledge"), serves to secure the continuous bond between the two higher powers of intellect–chochmah and binah; the lower level, referred to as da'at tachton ("lower knowledge") or da'at hamitpashet ("extending knowledge"), serves to connect the intellect as a whole with the realm of emotion, thereby enhancing one's determination and resolve to act in accordance with the essential truths that one has integrated into consciousness.
Of this level of da'at it is said (Proverbs 24:4): "the rooms are filled with da'at." "The rooms" are the chambers of the heart, the emotions of the soul (as alluded to by the word cheder, "room," which is an acronym for chesed din rachamim, the three primary emotions of the soul). The inner consciousness of da'at fills these rooms and enlivens them as does the soul to the body.
In the Zohar, this level of da'at is referred to as "the key that includes six." The "key" of da'at opens all six chambers (attributes) of the heart and fills them with lifeforce. Each of these six chambers, when filled with da'at, is referred to as a particular dei'ah ("attitude," from the root of da'at) of the soul.
Da'at = 474. Dei'ah = 79. 474 = 6 times 79–da'at includes (and generates) six dei'ot.
The spiritual state identified in Chassidut as corresponding to the sefirah of da'at is that of yichud ("unification").