However, when we compare the different levels, we say that the actual root revealed in and through the Sefirot is none other than Eyn Sof Himself. Even though intrinsically Eyn Sof is not revealed, He reveals to us what He wants. Accordingly, prior to the revelation of the Sefirot, they were subsumed under the name Eyn Sof, just like all the other powers encompassed within His limitless Will. However, when these attributes were revealed, they were no longer called Eyn Sof, for now they have an end and a limit, as mentioned above. Accordingly, they are called Sefirot, from the Hebrew root ספר (SaFaR) meaning to count or number, indicating that they have a measure and a limit.
How the Sefirot Channel the Unknowable Eyn Sof
Kalach Pitchei Chokhmah 6:10