Matthew Poole and continuators on Leviticus 23:38

38 Beside the sabbaths of the LORD and beside your gifts, and beside all your vows, and beside all your free-will-offerings, which ye give unto the LORD.

(i. e.) The offerings of the weekly sabbaths, by a Metonymy, as the day is sometimes put for the actions done in it, as Prov. 27. 1. 1 Cor. 3. 13. God will not have any sabbath sacrifice diminished because of the addition of others proper to any other feast. And it is here to be noted that though other festival days are sometimes called sabbaths, as here ver. 39. yet these are here called the sabbaths of the Lord, in way of contradistinction to other days of rest to shew that this was more eminently such than other feast-days, which also sufficiently appears from the fourth Commandement.

Which, being here distinguished from free-will-offerings made to the Lord, may seem to note what they freely gave to the Priests over and above their first-fruits and tithes or other things which they were enjoyned to give.