And Moses took half of the blood, and put it in basins
Half of the blood of the above sacrifices, this he put into basins, and set by, in order to sprinkle on the people:
and half of the blood he sprinkled on the altar;
the Targum of Onkelos adds, to atone for the people. But the altar here seems to represent the Lord, who was one of the parties covenanting, and therefore is sprinkled with blood as a ratification of the covenant on his part, and the promises of it.