Commentaries:
Though the author speaks specifically of the high priest, all priests who ministered before God were included within the scope of this law. Clearly, God is vitally concerned about the purity of heart, character, attitude, motive, and service of those who serve Him. Because we are to serve Him every day, this requires specific and continuing daily attention.
John W. Ritenbaugh
The Beatitudes, Part 6: The Pure in Heart
The Aaronic priesthood—including the high priest—was just as sinful as the population that they were to be serving. In order for this to be corrected, it was necessary that the true High Priest be one of divine nature, perfect, and sinless. Jesus Christ was both deity and humanity, and He qualified—through His sinlessness, His offering of His life, and His compassion—to be High Priest for the entirety of humanity. The book of Hebrews points out these things: 1) that He was divine, 2) that He offered His perfect life in sacrifice, and 3) that His mercy qualified Him to be High Priest.
Aaron's sons attained to the priesthood simply by being born into the Aaronic line. Members of the church, though, become priests by means of regeneration, making us part of the Divine Family—and thus brothers and sisters of Jesus Christ.
John W. Ritenbaugh
New Covenant Priesthood (Part One)