Cautions against error
The Lord has rendered my bonds light and easy since I learned that you are in peace, that you live in all harmony both of the flesh and spirit. “I therefore, the prisoner of the Lord, beseech you, that you walk worthy of the vocation wherewith you are called,” guarding against those heresies of the wicked one which have broken in upon us, to the deceiving and destruction of those that accept of them; but that you give heed to the doctrine of the apostles, and believe both the law and the prophets: that you reject every Jewish and Gentile error, and neither introduce a multiplicity of gods, nor yet deny Christ under the pretence of [maintaining] the unity of God.
Source: The Spurious Epistles (New Advent)