What does 2 Corinthians 6:15 mean?

Verses in this segment pose a series of questions to illustrate the reason behind the command that believers must not become "yoked" or harnessed to non-Christians. In the previous verse, Paul asked what fellowship light could have with darkness. The answer, of course, is that the two cannot co-exist. Once the light arrives, the darkness is gone.

Now Paul evokes the imagery of kingdoms or nations: asking what harmony there could ever be between Christ and Belial. Belial is another name for Satan, used only here in the Bible. The obvious answer is that Christ and Satan could never form a mutually beneficial agreement. They stand opposed to each other. More accurately, Belial the deceiver stands opposed to Christ, who is the Truth. When Christ arrives, all that is false must depart.

The question at hand, then, is how could a Christ-follower, a Christian, ever be united in any meaningful way with someone who is not a Christian? By definition, unbelievers are still under the authority of the god of this age who has blinded the minds of unbelievers (2 Corinthians 4:4). How could a believer and unbeliever ever pull together in a harness in the same direction? One would have to turn away from his or her appointed course.

Paul asks, as well, about the portion that will be given to believers and unbelievers. Believers share in all the unsearchable riches that belong to God (Ephesians 3:8). Unbelievers fall far short of receiving any of God's glory because they remain unforgiven for their sins (Romans 3:23). With such vastly different eternal destinies, how could a believer and unbeliever walk together in the same direction as required by the harness of a binding relationship?