Jesus Christ is the Head of his Body. His Body is the Church.
That pair of images is used to bring out a number of truths in the New Testament. For example, the truth that Christ directs his church as the head directs the body, and the truth that Christ is intimately connected to his church. Or within the church itself, the truth that each person is intimately related to each other person as different parts of the same body, and the truth that each has a particular role within the organic whole. The images work because they appeal to something which we understand and of which have experience. The images speak to us far more deeply and clearly than bare language (in so far as there is such a thing) ever could.
But the danger is that we let the image control the idea. We might conclude, for example, that because a head is as dependent on a body as a body is on a head, that Christ and his church stand in a reciprocal relationship of dependency. That won't do. Or we might construe the link between Christ and the church organically, as somehow natural, because this suits the image. We might then imagine that the church is in some way a continuation of the incarnation - after all, a head is only present with (and perhaps through) a body, so maybe Christ is present only in and through the church.
The image is illuminating in its original connection, in its right place in the argument. It is not therefore legitimate to develop it any which way, or to deploy it in wholly different contexts and arguments. Then it may well be only deceptive.
The image lives from the reality, and not vice versa.