Eph 5:5-13 How are we to understand what Paul says here?

Here Paul stresses the impossibility of anyone - including professing Christians - given to immorality, indecency, or the greed which makes an idol of gain, inheriting the kingdom of God and Christ. (Note the Deity of Christ confirmed by Paul here, declaring him equal ruler of the kingdom with God).

Christians must not allow themselves to be deceived by shallow excuses or arguments for sinning, because God's wrath will be poured out upon those who do them, whether they are professing Christians or not (CP 1Cor 6:18-20; Ga 5:19-21; Eph 4:17-19; Col 3:1-10; 1Th 4:1-7; He 12:14-15).

Christians used to be children of the darkness but now are children of the light and produce fruit of the spirit consisting of all forms of goodness, righteousness and truth. They do everything they can to please God and have nothing to do with the worthless things of the darkness. Instead, they expose or reprove the works of darkness for what they are by the light in which they walk (CP Eph 5:13).

This does not teach that everyone exposed to the light will become a Christians, rather it teaches that a holy Christian life reveals by contrast, the sinfulness of unregenerate lives (CP Jn 3:20-21 with Eph 5;14).