Audio commentary on this verse

Note 9 at Rom. 6:7: There is a difference between being "freed" and being "free." In the 1800's, President Lincoln issued the Emancipation Proclamation which "freed" the American slaves, but many slaves continued to serve their masters in slavery because the truth was hidden from them or in some cases, the slaves were afraid that they couldn't make it on their own.

Likewise, Christians have been "freed" from sin but that doesn't automatically mean all Christians experience that freedom. Through ignorance and deception, Satan continues to maintain mastery over those who have not yet realized their death and resurrection with Christ.