Charles H. Spurgeon on Psalms 110:4

Thou art a priest. The reasons which moved our Lord to take upon him the office of priest are conceived to be these.

1. Because the salvation and redemption of mankind, wrought by the sacrifice of his priesthood., being a most noble work, and not inferior to the creation, it was not fit that any should have the honour of it, but the Son of God.

2. Neither was it agreeable that any should offer him, who was the only sacrifice that could expiate the sins of the whole world, but himself: therefore by offering himself he added infinite worth to the sacrifice, and great honour to the priesthood of the Gospel.

For, as the gold sanctifieth not the altar, but the altar the gold; so it may be truly said without impeachment to the dignity of that calling, that Christ was rather an honour to the priesthood, than the priesthood an addition to him. For what got he by the priesthood which cost him his life? What preferment could it be to him, to take upon him an office, whereby he was to abase himself below himself, and be put to an ignominious and accursed death? What were we vile miscreants, conceived and born in original sin, and soiled with the filth of numberless actual transgressions, that to purge and cleanse our polluted souls and defiled consciences, the second person in the Trinity should be made a Priest? It was wonderful humility in him to wash his disciples feet; but in his divine person to wash our unclean souls, is as far above human conceit, as it seemeth below divine majesty. There is nothing so impure as a foul conscience; no matter so filthy, no corruption so rotten and unsavoury as is found in the sores of an exulcerated mind: yet the Son of God vouchsafed to wash and bathe them in his own blood. O bottomless depth of humility and mercy! Other priests were appointed by men for the service of God, but he the blood of beasts to save men, but he shed his own blood to save us, more like beasts than men: other priests offered sacrifice for themselves, he offered himself for a sacrifice: other priests were fed by the sacrifices which the people brought, but he feeds us with the sacrifice of his own body and blood: lastly, others were appointed priests but for a time, he was ordained a priest for ever. Daniel Featley.