Be on your guard against the snares of the devil
Not that I know there is anything of this kind among you; but I put you on your guard, inasmuch as I love you greatly, and foresee the snares of the devil. Wherefore, clothing yourselves with meekness, be renewed in faith, that is the flesh of the Lord, and in love, that is the blood of Jesus Christ. Let no one of you cherish any grudge against his neighbour. Give no occasion to the Gentiles, lest by means of a few foolish men the whole multitude [of those that believe] in God be evil spoken of. For, “Woe to him by whose vanity my name is blasphemed among any.”
Source: Epistle to the Trallians (New Advent)