He says not to walk or live as unbelievers do in the vanity of their own mind.   People can create all sorts of ideas in their own mind as to what life is all about.  They can deceive themselves as to what the truth really is.

Truth is truth whether we believe it or not.  Truth is truth whether we know about it or not.  We can’t just make up and decide for ourselves what truth is.   We can’t make up the rules that way.  Truth isn’t created within us.   Truth exists in God.  If we want to live according to the truth we need to seek God and find the truth that already exists.

In verse 18 he says unbelievers are alienated from the life of God because of the ignorance in them due to the blindness of their heart.  We who know the truth can live according to it.  God reveals it to us through His Word by His Spirit.

Confession:

Thank You Father God for showing me the truth so I can live according to it.  I submit to Your truth, to Your Word and to Your Spirit.  I will not walk in the vanity of an unbelieving mind.  I choose to believe You and Your ways are the ultimate truth.