The main theme of the letter to the Hebrews is to compare the sacrifice of Christ to the sacrifices of the priests of the Old Testament. The Old Testament priests made continual sacrifices of animals for themselves and the sins of the people, entering into the sanctuary of the Jerusalem temple. Christ makes the perfect and eternal sacrifice of Himself upon the cross, once and for all, for the sins of the people and not for Himself, entering into the heavenly sanctuary, not made by hands, "to appear in the presence of God on our behalf." (9:24)
The letter, to the Hebrews begins with the clear teaching about the divinity of Christ, affirming that God, Who "in many and various ways... spoke of old to our fathers" has "in these last days... spoken to us by a Son, Whom He appointed the heir of all things, through Whom He also created the world." (1:1-2)
Mostly, the letter to the Hebrews is read in the Orthodox Church at the divine liturgies during Great Lent.