(17) So this I say, and affirm together with the Lord, that you walk no longer just as the Gentiles also walk, in the futility of their mind,...
you did not learn Christ in this way, if indeed you have heard Him and have been taught in Him, just as truth is in Jesus, that, in reference to your former manner of life, you lay aside the old self, which is being corrupted in accordance with the lusts of deceit, and that you be renewed in the spirit of your mind, and put on the new self [nature], which in [the likeness of] God has been created in righteousness and holiness of the truth. (NASB95)

Here we see the Apostle Paul exhort the believer who confesses the Lord in this evil world. In contrast with the vain and ignorant life of the gentile world, the Apostle presents the life that follows from the knowledge of the truth found in Jesus Christ. Note the Apostle's use of Christ's personal name 'Jesus' which forces the reader to observe from the point of view of his or her personal path; the practical walk of a believer. We are to have in our mind the example Jesus has set. Our point of view is that of Jesus not of unbelievers. The truth explained here is that found in Jesus and is the truth of the new man, for Jesus Christ is the perfect expression of the new man that bears the character of God Himself. It is this example our new nature must mimic for the old man must be put aside. And only in this can we be righteous and holy.

Taken from Hamilton Smith's Ephesians