Hebrews 2:17

Wherefore in all things it behoved him to be made like unto
his brethren
The adopted sons of God, who were brethren before Christ's incarnation, being from all eternity predestinated to the adoption of children: Christ's incarnation was in time, and after that many of the brethren existed; and it was only for their sakes that he assumed human nature; and therefore it was proper he should be like them in that nature, in all things: in all the essentials of it; it was not necessary that he should have it by natural generation; nor that it should have a subsistence in itself as theirs: and in all the properties and affections of it, that are, not sinful; for it did not behove him to be like them in sin, nor in sickness, and in diseases of the body: and in all temptations; though in some things his differ from theirs; none of his arose from within; and those from without could make no impression on him: and in sufferings, that there might be a conformity between the head and members; though there is in some things a difference; his sufferings were by way of punishment, and were attended with wrath, and were meritorious, which cannot be said of theirs; but that he should have an human nature, as to its essence and perfection, like to theirs, was necessary: it was proper he should be truly and really man, as well as truly God,

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 say ^F16, (Nywv) , "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 leper ^F17: and the Jews tell us ^F18, 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.