Not all who call themselves Christians act like it. How should we think about them? Can Christians be worldly? The parable of the soils in Luke 8 shows that people have different responses to the gospel. Other Bible passages mention Christians who are not living correctly. 

Is it possible that some who call themselves Christians have lost their salvation? Maybe they were never really saved to begin with. It is possible that Christians can be immature in their spiritual growth and so also in their conduct. The Bible calls these "carnal" Christians or "babes in Christ." Perhaps these Christians have backslid or fallen back into sin or are struggling with sinful urges and habits. 

We should not deal with the problem of worldliness in Christians by changing the gospel to demand works or commitment up front or later as proof. These faulty gospels rob people of assurance of salvation. The best option is to teach a clear gospel of salvation by grace through faith in Jesus Christ who died for our sins and rose again and promises eternal life to all who believe in Him for it.

For more reading, checkout "The Reality of Carnal Christians" and "What about a Christian Who Doesn't Act Like One?"