How do we know that believers should not walk as Gentiles do?

In Ephesians 4:17-19, Paul urges the church at Ephesus to no longer walk as other Gentiles who are characterized by the vanity of their minds and a separation from the life of God. This warning is rooted in the identity of believers as those who have been called out of darkness into light. Such a radical transformation requires a distinct way of living, reflective of the newness of life bestowed upon them through Christ. The ignorance and blindness that define the unregenerate state contrast sharply with the understanding and spiritual enlightenment that believers possess, encouraging them to lead lives that are worthy of their calling.