Albert Barnes Commentary Numbers 9:11

"In the second month on the fourteenth day at even they shall keep it; they shall eat it with unleavened bread and bitter herbs:" — Numbers 9:11 (ASV)

The later Jews speak of this as the "little Passover." Coming, as it did, a month after the proper Passover, it afforded ample time for a man to purify himself from legal defilement, as also to return from any but a very distant journey. Compare Hezekiah's act (2 Chronicles 30:1–3).