Keil & Delitzsch, on Esth 9:26

“And since that time these days are called Phurim, that is, of lots: because Phur, that is, the lot, was cast into the urn. And all things that were done, are contained in the volume of this epistle, that is, of this book:”

“Wherefore they called these days Purim after the name Pur. This first על־כּן refers to what precedes and states the reason, resulting from what has just been mentioned, why this festival received the name of Purim. With the second על־כּן begins a new sentence which reaches to Est 9:28, and explains how it happened that these feast-days became a general observance with all Jews; namely, that because of all the words of this letter (of Mordochai, Est 9:20), and of what they had seen concerning the matter (על־כּכה, concerning so and so), and what had come upon them (therefore for two reasons: (1) because of the written injunction of Mordochai; and (2) because they had themselves experienced this event), the Jews established, and took upon themselves, their descendants, and all who should join themselves unto them (proselytes), so that it should not fail (i.e., inviolably), to keep (to celebrate) these two days according to the writing concerning them and the time appointed thereby year by year.”

Imported from an open dataset — not yet checked against the printed edition.