The Lord desires to make a covenant with us as human beings. In ancient times, a covenant was sealed with blood to signify that anyone who broke it would forfeit their life. As human sinners, we broke our covenant with the Lord. However, because God wants us to be close to Him, He provided a way of redemption even under the first covenant.
First, the high priest—who was himself a sinner—had to cleanse himself through blood sacrifices before entering the Holy of Holies to intercede for the people of Israel.
"He did not enter by means of the blood of goats and calves; but he entered the Most Holy Place once for all by his own blood, thus obtaining eternal redemption." — Hebrews 9:12
Hebrews 9 shows us that this earthly sanctuary was merely a shadow of the new covenant to come. Jesus offered His own blood and entered the true tabernacle in heaven, interceding on our behalf once and for all.