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In short, the reward of the priest’s labors will be in due proportion to the motives that urged his action.  If he seeks “the things which are his own” his reward will be an earthly one.  If he seeks “the things that are Christ’s” his reward will be an eternal one.  Again, if his motive be a selfish one, the results of his labors in the care of souls will be negligible, because the grace of God can be but scantily with him, but working with the motive of the love of God great results may be expected, because the grace of God will amply accompany his efforts.  For, with St. Paul, the priest who loves God sincerely may say:  “I can do all things in him who strengtheneth me” (Phil., iv, 13).  “For it is God who worketh in you (the faithful) both to will and to accomplish, according to his good will” (Phil., ii, 13).

Source: By Rev. Albert Rung: St. Paul, the Priest (The Homiletic Monthly and Pastoral Review) Vol. XXI Jan. 1921 No.4

(Special thanks to Bob Olson)

"The blessed Apostle Paul, wishing to describe the ideal Bishop and to form by his teachings a completely new man of the Church, explained what was, so to speak, his highest perfection. He stated that a Bishop must profess sure doctrine, in accordance with what has been taught, and thus be able to exhort others to sound doctrine and to refute those who contradict it."

Source: Saint Hilairy de Poitiers (De Trinitate)

"At that hour of the Sacrifice, at the words of the Priest, the heavens are opened, and in that mystery of Jesus Christ, the choirs of Angels are present, and things below are joined to things on high, earthly things to heavenly, and the service is both a visible and an invisible event."

Source: St. Gregory the Great

If it is true that by contemplating Christ sinners learn from him the “sorrow for sins” needed to bring them back to the Father, this is even more the case for sacred ministers.
How can we forget, in this regard, that nothing causes more suffering for the Church, the Body of Christ, than the sins of her pastors, especially the sins of those who become “thieves and robbers” of the sheep (cf. Jn 10:1 ff.), lead them astray by their own private teachings, or ensnare them in the toils of sin and death? Dear priests, the summons to conversion and to trust in God’s mercy also applies to us; we too must humbly, sincerely and unceasingly implore the heart of Jesus to preserve us from the terrifying risk of endangering the very people we are obliged to save.

Source: Pope Benedict XVI, Solemnity of the Sacred Heart of Jesus, 19 June 2009

"The entire Church cannot give to God as much honor, nor obtain so many graces, as a single priest by celebrating a single Mass; for the greatest honor that the whole Church without priests could give to God would consist in offering to Him in sacrifice the lives of all men."

Source: St. Alphonsus Liguori (The Dignity and Duties of the Priest)