Jamieson, Fausset and Brown on Numbers 9:8-14

8-14. Moses said unto them, Stand still, and I will hear what the Lord will command concerning you--A solution of the difficulty was soon obtained, it being enacted, by divine authority, that to those who might be disqualified by the occurrence of a death in their family circle or unable by distance to keep the passover on the anniversary day, a special license was granted of observing it by themselves on the same day and hour of the following month, under a due attendance to all the solemn formalities. (See on 2Ch 30:2). But the observance was imperative on all who did not labor under these impediments.