Long ago there was a theory that dinosaurs grew to huge sizes because reptiles grow to fit the environment, for the same reason that Galapagos tortoises are so large. There were several things wrong with this theory. It doesn’t account for different sizes of dinosaur (brachiosaur vs T. Rex). Dinosaurs have since been classified as avian rather than reptilian. And the theory that reptile size is limited by environment has been proven wrong. Just try to keep a Nile crocodile in a 40-gallon tank. Even the theory of island gigantism, as in the Galapagos or Aldabra tortoises, has taken a genetic hit; they may be descendants of mainland giants. The theory that size can be limited by putting a reptile in a small tank, though, does have some spiritual applications.
Some Christians live within a tank with four walls. The size of the church building never increases. They go outside the building weekly, but their religion stays inside, and it never grows larger than the building in which it is housed. Are they Christians? Undoubtedly. We must grant them that, because that is something from God. They are not “so-called” Christians. They are not dead Christians. They may be weakened by their environment. If you put an iguana in a small tank it will become stressed and get sick, or even die. So it is with those whose Christianity stays within the confining limits of the church building. They are like those Paul spoke of who take the Lord’s Supper in an unworthy manner.
But let a man examine himself, and so let him eat of that bread, and drink of that cup. For he that eateth and drinketh unworthily, eateth and drinketh damnation to himself, not discerning the Lord's body. For this cause many are weak and sickly among you, and many sleep. (1 Cor 11:28-30)
On the other hand, even caged animals should be taken out and exercised. Their enclosures should be enlarged to grow with them, rather than limiting them to the same space. In like manner, the assembly is meant as a temporary resting place. It is not the totality of our Christianity. It serves a purpose, but that purpose is just a beginning.
And let us consider one another to provoke unto love and to good works: Not forsaking the assembling of ourselves together, as the manner of some is; but exhorting one another: and so much the more, as ye see the day approaching. (Heb 10:24-25)
Church, the body of believers, is a place of encouragement and training. We provoke and exhort. The love and good works are not limited to those within the body. In fact, it is those without that may need them more. It is in going outside the walls of the church building that we grow as we should. Our Christianity is a daily thing, not something to be put in a box and taken out once, twice, or thrice a week.
The assembly of the church is not intended to be a limiting tank, where we keep our Christianity in the hope that it doesn’t outgrow us. If we try to keep it in, it will either get sick and die or it will break the walls. If we are to grow in a healthy manner, we must expand beyond the limits of the congregational assembly. The dinosaurs may have grown large because they were large. We may grow large because that is the will of God.