The right, left and center columns refer to a certain manner in which the sefiros relate to each other.

The right column (chochma, chessed, netzach) are characterized by an outward expression, or hispashtus.

The left column (binah, g’vura, hod) is characterized by limitation, discipline, and tzimtzum.

The right column reflects masculinity. The left column reflects femininity. The middle column reflects the Infinite One who is the only one who can make opposites attract and remain united actually as one.

See Z”a.