Hebrews 5:6

As he saith also in another place, Thou art a priest for ever after the order of Melchisedec.

Christ did not exalt Himself to become High Priest but was called and declared by God to be a priest permanently in the order of Melchizedek, not through human arrangement or self-claim. His priesthood began when humanity sinned, so that although the race came under death it was given hope instead of being left to perish, a hope expressed in Eden in the promise that the woman's seed would crush the serpent's head while having His own heel bruised. The earthly high priest was specially designed to represent Christ. Christ's priesthood is permanent and unending, never passing to another holder or being replaced.

By contrast, many high priests serving before and at Christ's advent were not divinely appointed but sought the office from ambition and love of power and obtained it by bribery or murder. Though exalted, Christ came in humility, veiling His divinity with humanity and becoming one with the human family. In the days of His earthly life He offered prayers and earnest pleas with intense emotion and tears to the One able to save Him from death, and He was heard because of His reverent submission. Though He was Son, He learned obedience through what He suffered and, being made complete, became the source of eternal salvation for all who obey Him.

Having been tempted in every way as human beings are yet without sin, He is moved by human weakness, has compassion on the ignorant and straying, knows how to rescue those assailed by powers of darkness, and will never separate from anyone who trusts Him. Those who live in His presence should therefore hold firmly to their confession of faith and come confidently to the throne of grace to receive mercy and help in need. Remembering His compassion, believers when provoked by perverse and stubborn fellow believers should restrain the tongue from wounding words that injure Christ in the person of His family members. The verse sets forth the only conditions for being saved in God's appointed way: learning obedience and humility as little children, letting genuine obedience soften and subdue the heart, doing God's works, becoming willing to learn every lesson, and abandoning the idea that one may exalt or abase at pleasure, for without this God cannot accept a person's labors or save.