An excerpt from the Sermon of St. Leo the Great.

I rejoice, dearly beloved, in the pious affection of your devotion, and I gave thanks to God that I see in you the love of Christian unity.  For your very presence here testifies that you understand that the annual return of this day is a matter for common rejoicing; and that in celebrating the annual festival of the Shepherd, you are honoring the whole flock. For though the universal Church is ordered in varying degrees, so the whole is made up from the diverse members of the sanctified Body, we are all, nevertheless. as the Apostle says, one in Christ; and no one is separated by his office from another, so that even the least amongst us is related to the head. Therefore, Beloved, in to the words of the blessed Peter, spoken by his own consecrated voice:  Be you as living stones built up, a spiritual house, a holy priesthood, to offer up spiritual sacrifices, accepted to God by Jesus Christ.  And a little later:  You are a chosen generation, a kingly priesthood, a holy nation, a purchased people.