How is the body of Christ related to Christ?

The body of Christ is the complement of Christ, just as Eve complemented Adam. Christ is still waiting for it and looking for it, and when it is suddenly filled with the last one brought in, He will take it to Himself.

Les explains that God said it was not good for man to be alone and made him a help mate, a complement. Eve was the complement that completed Adam in that relationship, and the body of Christ is likewise Christ's complement. Les says Christ is still waiting for and looking for it; when it is suddenly filled and the last one is brought in, He will take it to Himself. Revelation 19 speaks of the marriage of the Lamb, and Les prefers "bride" to "wife," because the fine linen is the righteousness, or positional aspect, of the saints. Then Christ comes the second time to the Mount of Olives as King of kings and Lord of lords.

Genesis 2:18

And the LORD God said, It is not good that the man should be alone; I will make him an help meet for him.

In what sense is the body of Christ Christ's complement?

The body of Christ is Christ's complement in the same sense Eve completed Adam: it is the counterpart that completes Him in relationship. Christ is still waiting for and looking for this complement, and when it is suddenly filled and the last one is brought in, He will take it to Himself.