The term "halt you" in the King James' Version ("falter," NKJV) provides a literal picture of what Elijah means. It suggests a person staggering, unable to catch his balance, and failing to accomplish anything of any consequence because his mind is divided. The person in such a circumstance cannot get a grip on life. These people were wavering back and forth, which was typical of the Israelites. The Bible shows in many places that the people continued to worship God, yet also served their idols. In Exodus 32, the incident of the Golden Calf, the people had Aaron mold a calf of gold and proclaim a feast to the Lord!
Essentially, they tried to syncretize the true God and pagan idols, which suggests a divided mind. "No man can serve two masters; for . . . he will hate the one and love the other" (Matthew 6:24). But the one that he hates is still a part of his mind, and it will cause problems.
In Elijah's word-picture, he is indicating that though nothing is wrong with the rest of the body, because the mind has no focus, the body's efforts have no direction. This sets up a situation where, at best, there will be little movement—that is, little accomplished—and at worst, there will be no forward movement at all, but just staggering, first this way then that. That sort of situation produces nothing.