פירוש על במדבר 7:16

שעיר עזים אחד לחטאת ONE KID OF THE GOATS FOR A SIN-OFFERING, to make expiation for uncleanness caused by a grave in the depths of the earth, (i.e. one that is not known to exist and it might therefore be assumed that people passed over it and thereby unwittingly became unclean), which was only a doubtful uncleanness (one about which there exists a doubt as to whether it actually has been incurred or not) (cf. Sifrei Bamidbar 51).

To atone for the grave of the abyss. Meaning of “the grave of the abyss” is when one did not realize about at all, as if it had been buried in the abyss where a person does not think that there may be a grave. It was still necessary for them to purify themselves from this “impurity” and from contact with a doubtful impurity. If they did not then they would not be permitted to come to the sanctuary or to the courtyard because their doubtful impurity that can be atoned for by way of the he-goat sin-offering must be atoned for. However a definite impurity would be overridden by a communal offering such as the Pesach-offering, this overrides impurity if most of the community are impure, as the Torah writes “in its time” — even in impurity. Re’em expands upon this, but I have been brief.