Hebrews 10:1; Hebrews 10:3-4; Hebrews 10:8
The old plan was only a hint of the good things in the new plan. Since that old "law plan" wasn't complete in itself, it couldn't complete those who followed it. No matter how many sacrifices were offered year after year, they never added up to a complete solution.
But instead of removing awareness of sin, when those animal sacrifices were repeated over and over they actually heightened awareness and guilt.
The plain fact is that bull and goat blood can't get rid of sin.
When he said, "You don't want sacrifices and offerings," he was referring to practices according to the old plan.