Church vs Cancer

I read this a few days ago and it stuck with me...

When you ask what is the purpose of making converts, the answer is, so they can make more converts, and when you ask what is the purpose of those further converts, it is so they can make more converts. There is, in others words, an infinite regress. And, as we know from the medical analogy, the multiplication of cells unrelated to the purpose of the body is what we call cancer.... I do think that a very sharp criticism needs to be made against the idea that the Church exists simply to make more members, irrespective of the purpose for which the Father sent the Son into the world, which is that the presence of the reign of God might be a reality now. - Lesslie Newbigin (A Word in Season, p58)