John Gill Commentary Numbers 15:25

"And the priest shall make atonement for all the congregation of the children of Israel, and they shall be forgiven; for it was an error, and they have brought their oblation, an offering made by fire unto Jehovah, and their sin-offering before Jehovah, for their error:" — Numbers 15:25 (ASV)

And the priest shall make an atonement for all the
congregation of the children of Israel ;
&c.] By offering a sin offering for them, a type of Christ, the propitiation not only for the sins of the people among the Jews, but throughout the whole world, (1 John 2:2) ;

and it shall be forgiven them ;
as the sins of the Lord's people are forgiven them through the blood of Christ, and on account of his stoning sacrifice and satisfaction made for them:

for it [is] ignorance ;
a sin of ignorance, for which reason Christ pleads for pardon on the foot of his sacrifice, and his people receive it, (Luke 23:34) (1 Timothy 1:13) ; for that this sin was forgiven on the score of a sacrifice appears by what follows:

and they shall bring their offering, a sacrifice made by fire unto the
Lord ;
the bullock for the burnt offering:

and their sin offering before the Lord, for their ignorance ;
a kid of the goats.