5 For if any one will consider how great a thing it is for one, being a man, and compassed with flesh and blood, to be enabled to draw near to that blessed and pure nature, he will then clearly see what great honor the grace of the Spirit has vouchsafed to priests; since by their agency these rites are celebrated, and others nowise inferior to these both in respect of our dignity and our salvation. For they who inhabit the earth and make their abode there are entrusted with the administration of things which are in Heaven, and have received an authority which God has not given to angels or archangels.
For it has not been said to them, “Whatsoever you shall bind on earth shall be bound in Heaven, and whatsoever you shall loose on earth shall be loosed in Heaven.” They who rule on earth have indeed authority to bind, but only the body: whereas this binding lays hold of the soul and penetrates the heavens; and what priests do here below God ratifies above, and the Master confirms the sentence of his servants. For indeed what is it but all manner of heavenly authority which He has given them when He says, “Whose sins ye remit they are remitted, and whose sins ye retain they are retained?” What authority could be greater than this?
“The Father has committed all judgment to the Son?” But I see it all put into the hands of these men by the Son. For they have been conducted to this dignity as if they were already translated to Heaven, and had transcended human nature, and were released from the passions to which we are liable. Moreover, if a king should bestow this honor upon any of his subjects, authorizing him to cast into prison whom he pleased and to release them again, he becomes an object of envy and respect to all men; but he who has received from God an authority as much greater as heaven is more precious than earth, and souls more precious than bodies, seems to some to have received so small an honor that they are actually able to imagine that one of those who have been entrusted with these things will despise the gift.
Away with such madness! For transparent madness it is to despise so great a dignity, without which it is not possible to obtain either our own salvation, or the good things which have been promised to us. For if no one can enter into the kingdom of Heaven except he be regenerate through water and the Spirit, and he who does not eat the flesh of the Lord and drink His blood is excluded from eternal life, and if all these things are accomplished only by means of those holy hands, I mean the hands of the priest, how will any one, without these, be able to escape the fire of hell, or to win those crowns which are reserved for the victorious?
Source: On the Priesthood (New Advent)