The office of high priest was one of honor; yet, the high priest, as a human being, was subject to human frailities.
Yet, boldness was required. The high priest was approaching God to ask for mercy and grace for the sinful and suffering.
Not just anybody could be a high priest. Rather, only God could decide who would be appropriate for the role.
The author of this letter is pointing out that Jesus is the high priest for Christians. He, as human, can sympathize with our human condition. And, and Son of God, having been made perfect, he is the source of eternal salvation.