IV. This festival then is in St. Peter's honour, and the progress of his flock redounds to his glory
And so, dearly beloved, with reasonable obedience we celebrate today's festival by such methods, that in my humble person he may be recognized and honoured, in whom abides the care of all the shepherds, together with the charge of the sheep commended to him, and whose dignity is not abated even in so unworthy an heir. And hence the presence of my venerable brothers and fellow priests, so much desired and valued by me, will be the more sacred and precious, if they will transfer the chief honour of this service in which they have deigned to take part to him whom they know to be not only the patron of this see, but also the primate of all bishops.
When therefore we utter our exhortations in your ears, holy brethren, believe that he is speaking whose representative we are: because it is his warning that we give, nothing else but his teaching that we preach, beseeching you to “gird up the loins of your mind,” and lead a chaste and sober life in the fear of God, and not to let your mind forget his supremacy and consent to the lusts of the flesh. Short and fleeting are the joys of this world's pleasures which endeavour to turn aside from the path of life those who are called to eternity.
The faithful and religious spirit, therefore, must desire the things which are heavenly, and being eager for the Divine promises, lift itself to the love of the incorruptible Good and the hope of the true Light. But be sure, dearly-beloved, that your labour, whereby you resist vices and fight against carnal desires, is pleasing and precious in God's sight, and in God's mercy will profit not only yourselves but me also, because the zealous pastor makes his boast of the progress of the Lord's flock.
“For you are my crown and joy,” as the Apostle says; if your faith, which from the beginning of the Gospel has been preached in all the world has continued in love and holiness. For though the whole Church, which is in all the world, ought to abound in all virtues, yet you especially, above all people, it becomes to excel in deeds of piety, because founded as you are on the very citadel of the Apostolic Rock, not only has our Lord Jesus Christ redeemed you in common with all men, but the blessed Apostle Peter has instructed you far beyond all men. Through the same Christ our Lord.
Source: Sermons (New Advent)