“All the body … grows.” (Colossians 2:19)
Make sure you keep growing for the sake of the whole body. “Oh!” you say, “I do not know that I want to grow. I have believed in Christ, and I am saved, and that is enough for me.” But, my dear friend, you must grow because the whole church of Christ is supposed to grow. Suppose that when I was a young boy one of the bones in my arm had refused to grow. If all the rest of the body had been properly developed, what would have happened if that particular bone did not grow? Why, I would have had a short arm. Suppose that one of the bones of your leg had said to itself, “I am in the body, and that is enough for me. I do not intend to grow any more.” You would have had to go hopping through the world with one short leg all your life. That would have been a very uncomfortable thing for you, and you probably would have had great pain as well as inconvenience. So, if one Christian in the church does not grow, he will cause trouble for the others. The brother next to him is growing, and it makes it very awkward when some progress and others do not.
From Spurgeon on Unity, pp. 57