In a sermon on this passage, specifically verse 23, Lloyd-Jones writes...
"We now recognize that becoming a Christian does not mean that you simply change your moral suit or your outward behaviour. Nor does it merely mean that you change your opinions, or change your mind. But it most certainly means changing the spirit of your mind. What a distinction! In other words, Christianity is not something that you and I take up intellectually; it is something that takes us up, and captivates us, and governs us, and controls us."
"The Christian is tested, not simply by what he says, not simply by the opinions he puts forward, but by the spirit of his mind. We must take Paul's message to heart. If the spirit of our mind is changed and is renewed, we shall be thinking in such a way that we shall put off the old man, and will put on the new man."
~ Martyn Lloyd-Jones, Darkness and Light: An Exposition of Ephesians 4:17--5:17, p 165-66.
The original sermon can be streamed or downloaded from here.