Recommended Book: First Epistle of Clement to the Corinthians - Kindle Edition (get Kindle app for phone) (paid link)

If then you adhere to the ancient faith, and which has been transmitted to us by the holy fathers; if your sentiments, like ours, correspond with those which they entertained concerning the Incarnation of the Lord our Savior, and if you in nothing deviate from the doctrine of the universal church... this faith let us mutually hold in sincerity of mind and truth of heart, and there is peace. Let us also keep inviolate the rules which the church has received from those same fathers, and there is peace. Let this be a thing certain and fixed, and there is no discord.

Gelasius, Pope [regn. A.D. 492-496]