Augustine of Hippo in s. 78.6, a sermon on the Transfiguration of the Lord.
Augustine’s message applies to all Christians in their vocation, but it applies most poignantly to Holy Church’s pastors.
And in this glory [of the Lord transfigured] is fulfilled what He has promised to those who love Him: “he who loves me will be loved by My Father, and I will love him.” … Great gift! great promise! God holds for you nothing less than Himself. O you covetous one; why isn’t Christ’s promise enough for you? You seem to yourself to be rich; yet if you do not have God, what do you have? Another person is poor, yet if he has God, what does he lack?
Come down, Peter! You wanted to rest on the mount. Come down and “preach the word, be instant in season, out of season, reprove, rebuke, exhort with all longsuffering and doctrine.” Persevere, work hard, bear your measure of torture — so that you might possess what is meant by the white garment of the Lord, through the brightness and the beauty of an upright labor in charity.
[…] Hear and listen, O covetous one: the Apostle explains clearly to you in another place: “Let no man seek his own, but another’s.” He says of himself, “Not seeking mine own profit, but the profit of many, that they may be saved.” This Peter did not yet understand when he desired to live on the mount with Christ. He was reserving this for you, Peter, after death.
But for now He says, “Come down, to labor on the earth; on the earth to serve, to be despised, and crucified on the earth.
The Life came down, that He might be slain; the Bread came down, that He might hunger; the Way came down, that life might be wearied in the way; the Fountain came down, that He might thirst; and yet you refuse to work?
Seek not your own. Have charity, preach the truth; so shall you come to eternity, where you shall find security.”