Numbers 31:51

51.And Moses and Eleazar the priest took the gold. It was fitting that this should be added, lest any should suppose that Eleazar made a profit by the liberality of others. Moses, therefore, relates, that whatever gold was offered, was faithfully laid up as an ornament for the sanctuary. When it is said, “for a memorial for the children of Israel,” it may be taken either actively or passively; viz., either that the gift may be a monument of their gratitude, or that it might conciliate favor for the people in the eyes of God; as if that offering of expiation brought before God, and represented, all those who thus professed themselves to be preserved by His grace. I prefer the latter sense myself, i.e., that this memorial was set before His eyes, in order that God might hereafter also be favorable to His people.