Albert Barnes on Ephesians 4:23

And be renewed. That is, it is necessary that a man who has been following these should become a new man. Jn 3:3, seq. Comp. 2Cor 4:16. The word here used--ανανεοω--does not occur elsewhere in the New Testament; but it has the same meaning as the word used in 2Cor 4:16, and Col 3:10. It means to make new, and is descriptive of the work of regeneration. This was addressed to the church, and to those whom Paul regarded as Christians; and we may learn from this,

(1.) That it is necessary that man should be renewed in order to be saved.

(2.) That it is proper to exhort Christians to be renewed. They need renovated strength every day.

(3.) That it is a matter of obligation to be renewed. Men are bound thus to be renovated. And

(4.) that they have sufficient natural ability to change from the condition of the old to that of the new man, or they could not be exhorted to it.

In the spirit of your mind. In your temper; your heart; your nature.

(b) "in the spirit" Rom 12:2