Similarly, limitlessness includes limitations and boundaries – in the sense that it is their very negation. This is the way in which the Sefirot exist in Eyn Sof, blessed be He. For the entire way in which He acts now – within boundaries and limitations – was already conceived on the plane of limitlessness as a hypothetical possibility that was, however, negated by His very limitlessness. If so, the finite existed in the infinite as a hypothetical possibility. When Eyn Sof wanted His intrinsic limitlessness not to touch this part, it came into being in the way that it exists now, within limits.
Account of Eyn Sof
Kalach Pitchei Chokhmah 24:13