Roman Catechism 4.16

Chapter 4 — Part I: The Creed — Article II: And in Jesus Christ, His Only Son, Our Lord

Section 16. Christ was also a Priest, not indeed of the same order as were the priests of the tribe of Levi in the Old Law, but of that of which the Prophet David sang: Thou art a priest for ever according to the order of Melchisedech. This subject the Apostle fully and accurately develops in his Epistle to the Hebrews.