On Communion with the Heterodox

St. Athanasius of Alexandria ca. 297-373

I have been compelled, at the instance of certain most sincere brethren, to write at once in order that keeping faithfully and without guile the pious faith which God’s grace works in you, you may not give occasion of scandal to the brethren. For when any sees you, the faithful in Christ, associate and communicate with such people, [or worshipping along with them], certainly they will think it a matter of indifference and will fall into the mire of irreligion. Lest, then, this should happen, be pleased, beloved, to shun those who hold the impiety [of Arius], and moreover to avoid those who, while they pretend not to hold with Arius, yet worship with the impious. And we are specially bound to fly from the communion of men whose opinions we hold in execration. [If then any come to you, and, as blessed John 2 Jn. 10 says, brings with him right doctrine, say to him, All hail, and receive such an one as a brother.] But if any pretend that he confesses the right faith, but appear to communicate with those others, exhort him to abstain from such communion, and if he promise to do so, treat him as a brother, but if he persist in a contentious spirit, him avoid. (Letter 53)