God's provision of an animal sacrifice for forgivness of sins is an expression of mercy because it taught the Jews all about sin,forgiveness,confession of
sin,the cost of sin.God's holiness and prepared them for the one to come,
a perfect sacrifice who would die for sin.
Animal sacrifices did not actually atone for sin. Hebrews 10:4 tells us that.
Man needs someone greater than himself to pay for his sin.