A homeless man, as I dismissed him from the parish perpetual adoration chapel where I am a priest, in which he lay on the pew, sleeping, shoes off--with the resulting persistent stench--exclaimed "you ain't priest material." For 24 hours I thought about that idea. Then it occurred to me that he is right. Here's why.
It's in the very nature of the Sacrament. Christ alone is the Priest Material! My ministry, if it is real, is not my own. I belong to another. The "priest material" is not one's own. No one, only Christ, is priest material.
That is what the Church means by calling ordination to the ministry of priesthood a "sacrament." Here is how Joseph Ratzinger says it.
"This man is in no way performing functions for which he is highly qualified by his own natural ability nor is he doing the things that please him most and that are most profitable. On the contrary, the one who receives the sacrament is sent to give what he cannot give of his own strength; he is sent to act in the person of another, to be his living instrument. For this reason no human being can declare himself a priest; for this reason, too, no community can promote a person to this ministry by its own decree. Only from the sacrament, which belongs to God, can priesthood be received. Mission can only be received from the one who sends, from Christ in His sacrament, through which a person becomes the voice and the hands of Christ in the world. This gift of himself, this renunciation and forgetfulness of self does not however destroy the man; rather, it leads to true human maturity because it assimilates him to the Trinitarian mystery and it brings to life the image according to which we were created. Since we were created in the image of the Trinity, he who loses himself will find himself... According to the Gospels Christ Himself handed on the essential structure of His mission to the apostles, to whom He grants His power and whom He associates with His power. This association with the Lord, by which a man receives the power to do what he cannot do alone is called a sacrament. The new mission created in the choosing of 12 men has a sacramental nature. This structure flows, therefore, from the center of the biblical message. It is obvious that this ministry created by Christ is altogether new and is in no way derived from the Old Testament, but arises from Jesus Christ with new power. The sacramental ministry of the Church expresses the novelty of Jesus Christ and His presence in all phases of history."
Joseph Cardinal Ratzinger, "The Nature of the Priesthood," October 1, 1990 Speech, in The Essential Pope Benedict XVI: His Central Writings and Speeches, eds. Thornton and Varenne, New York: Harper One, 2008, 297-298.
Also at https://www.catholicculture.org/culture/library/view.cfm?id=874.