that he might be a merciful and faithful high priest; he could not be an high priest, offer sacrifice for sin, and make intercession, unless he was man; nor could he be a "merciful" and compassionate one, sympathize with his people in their sorrows, temptations, and sufferings, unless he was like them in these; nor would he be a "faithful", that is, a true and lawful one otherwise, because every high priest is taken from among men:
in things pertaining to God; in things in which God has to do with his people, as to preside in his name over them, to declare his will unto them, and bless them; and in things in which the people have to do with God, to offer to God a sacrifice for their sins, to present this sacrifice to him, to appear in his presence for them, to carry in their petitions, and plead their cause as their advocate:
to make reconciliation for the sins of the people; of God's covenant people, the people he has chosen for himself, and given to his Son; and whom Christ saves from their sins, by making satisfaction for them, to the law and justice of God, which is here meant by reconciliation: and in order to this, which could not be done without blood, without sufferings and death, it was proper he should be man, and like unto his brethren: the allusion seems to be to the two goats on the day of atonement, one of which was to be slain, and the other let go; which were to be, as the Jews sayF16, שוין, "alike", in colour, in stature, and in price; and so were the birds to be alike in the same things, that were used at the cleansing of the leperF17: and the Jews tell usF18, that the high priest was to be greater than his brethren, in beauty, in strength, in wisdom, and in riches; all which is true of Christ.
Gill, John. "Commentary on Hebrews 2:17". "The New John Gill Exposition of the Entire Bible". https://www.studylight.org/commentaries/geb/hebrews-2.html. 1999.