The Kabbalistic Tree of Life arranges its ten sephirot into three vertical columns, and the rightmost of the three, running from Chokmah at the top through Chesed and down to Netzach, is called the Pillar of Mercy, taking its name from Chesed, whose own title is simply Mercy in most translations of the sephirotic names. Kabbalistic and later ceremonial magical literature treats this column as expressing an active, expansive, outward-flowing quality, traditionally gendered masculine in the older sources and associated with growth, generosity and unrestrained force, in contrast to the restrictive, form-giving quality assigned to the pillar opposite it.
The three-column arrangement itself, sometimes called the Pillars of the Tree or the Three Pillars, is at least as old as the classical Kabbalistic diagrams of the Tree of Life and became one of the structure's most frequently reproduced organizing features, since grouping the ten sephirot into three columns of three, three and three, with Malkuth hanging below the Middle Pillar as a tenth point, gives the whole diagram a visual and conceptual symmetry that a simple linear list of ten sephirot lacks entirely. This arrangement, sometimes called the Pillars of Severity, Mercy and Mildness by later writers who name the Middle Pillar with the third term, is read by most Kabbalists as a permanent structural fact about the Tree rather than as an optional interpretive overlay, since the column groupings follow directly from the paths already drawn between the sephirot in the oldest surviving diagrams.