John Gill Commentary Numbers 15:8

"And when thou preparest a bullock for a burnt-offering, or for a sacrifice, to accomplish a vow, or for peace-offerings unto Jehovah;" — Numbers 15:8 (ASV)

And when you prepare a bullock [for] a burnt offering
Which was a larger offering, and required a larger meat offering and drink offering, as (Numbers 15:9Numbers 15:10) show:

or [for] a sacrifice in performing a vow or peace offerings to the
Lord ;
by which latter are meant freewill offerings; for though both sorts here mentioned were peace offerings, yet these were more particularly called so.