This I say therefore, and testify in the Lord - I bear witness in the name of the Lord Jesus, or ministering by his authority. The object of this is, to exhort them to walk worthy of their high calling, and to adorn the doctrine of the Saviour. With this view, he reminds them of what they were before they were converted, and of the manner in which the pagan around them lived.
That ye henceforth walk not - That you do not henceforth live - the Christian life being often in the Scriptures compared to a journey.
As other Gentiles walk - This shows that probably the mass of converts in the church at Ephesus were from among the pagan, and Paul regarded them as Gentile converts. Or it may be that he here addressed himself more particularly to that portion of the church, as especially needing his admonition and care.
In the vanity of their mind - In the way of folly, or in mental folly. What he means by this he specifies in the following verses. The word “vanity” in the Scriptures means more than mere “emptiness.” It denotes moral wrong, being applied usually to those who worshipped vain idols, and then those who were alienated from the “true” God.