The central focus of the Book of Hebrews is on God’s provision of a “Great High Priest” and a “perfect sacrifice” who would be required for the eternal forgiveness of mankind’s sins. (hisspirit.org)
Israel’s sin had continually interrupted God’s fellowship with His chosen and covenant people, Israel. (Life Application Study Bible)
Under the Old Covenant, given under Moses, God had graciously and sovereignly established a system of sacrifices that symbolically represented the repentance of His chosen people and God’s cleansing and forgiveness of their sins. (hisspirit.org)
However, the need for sacrifices never ended because both the people and the Levitical priests continued to sin.
The need of all mankind was for a perfect high priest and a perfect sacrifice that would actually remove sin.
That God’s provision of a perfect high priest and a perfect sacrifice would be found in Jesus is the central message of the Book of Hebrews.
Generally, the epistle to the Hebrews is a study in contrast.
Read More on Hebrews Chapter 4