"1 For every high priest taken from among men is ordained for men in things pertaining to God, that he may offer both gifts and sacrifices for sins:
2 Who can have compassion on the ignorant, and on them that are out of the way; for that he himself also is compassed with infirmity.
3 And by reason hereof he ought, as for the people, so also for himself, to offer for sins.
4 And no man taketh this honour unto himself, but he that is called of God, as was Aaron."
...........................Hebrews 5:1-4

..............The High Priest, under the Law, had to have compassion upon the ignorant and on them that were out of the way, because he was conscious of his own infirmities.

........................................The fact of his being a sinner himself was one qualification for the priesthood.