There are two ways a body can grow.
A living thing scales by multiplication. A cell divides, and each new cell contains the whole machinery — everything required to feed itself, maintain itself, and divide again. Growth adds fully equipped units. This is how the New Testament church scaled: a household filled, and planted another household, and the new one had the full relational machinery of the old.
An empire scales by annexation. It moves a border. The population inside the new border is added to the whole without being changed by it — same villages, same customs, same loyalties, same gods, now under new administration. Annexation adds governed subjects, not formed members.
Hold that distinction, and watch Israel, because Scripture ran the experiment first and recorded the result without flinching.
Every ingathering imports gods
Every time the people of God gathered in a new population, the population brought its gods. Every time.
Jacob's own household, at the beginning: Then Jacob said unto his household, and to all that were with him, Put away the strange gods that are among you (Genesis 35:2). The founding family is carrying idols in the baggage.
The exodus generation: within weeks of Sinai they have made a calf, and Stephen's commentary is exact — in their hearts turned back again into Egypt (Acts 7:39). They left Egypt. Egypt's gods travelled with them, inside.
Joshua's last assembly, a lifetime later, after the Jordan and Jericho and the whole conquest: put away the gods which your fathers served on the other side of the flood, and in Egypt; and serve ye the LORD (Joshua 24:14). Still. The command at the covenant renewal is still put away the gods, because the gods had come the whole way.
The conquest was fenced with warnings about exactly this: They shall not dwell in thy land, lest they make thee sin against me: for if thou serve their gods, it will surely be a snare unto thee (Exodus 23:33). And Judges records the warning ignored — a whole first chapter listing the peoples not driven out, then the verdict:
And they forsook the LORD God of their fathers, which brought them out of the land of Egypt, and followed other gods, of the gods of the people that were round about them. (Judges 2:12)
Annexed peoples, retained gods, and the gods flowed uphill into the annexing nation.
The most exact case in Scripture
Then a precise instance, because it's conquest importing the conquered gods in one verse.
Next, it came to pass, after that Amaziah was come from the slaughter of the Edomites, that he brought the gods of the children of Seir, and set them up to be his gods, and bowed down himself before them, and burned incense unto them. (2 Chronicles 25:14)
He conquered a nation and adopted the gods of the nation he had just beaten. And the prophet's question is the question this whole article asks:
Why hast thou sought after the gods of the people, which couldn't deliver their own people out of thine hand? (2 Chronicles 25:15)
Scale won. Gods imported. Even in victory — especially in victory.
Solomon is the same mechanism through alliance instead of war. Seven hundred wives, princesses (1 Kings 11:3) — which is to say, seven hundred treaties, the ancient method of scaling a kingdom. And every treaty carried a god, until the man who built the temple was building high places for Chemosh and Molech on the hill facing it, and likewise did he for all his strange wives (1 Kings 11:8). The kingdom scaled by alliance, and the alliances brought their altars.
The formula
When Assyria resettled foreign populations into Samaria, they were taught the religion of the land and adopted it. The historian gives his verdict twice so nobody can miss it:
They feared the LORD, and served their own gods. (2 Kings 17:33)
So these nations feared the LORD, and served their graven images. (2 Kings 17:41)
Both at once. The name of the LORD added on top; the old gods retained underneath; the two running concurrently for generations. That's what a population looks like when it has been added to the people of God without being formed by him.
The church runs the same experiment
Under the household form, entry had a border, and the border was formative. Years of instruction. Sponsors who vouched. At baptism, a renunciation spoken aloud: the candidate renounced the devil, his works, and his pomp — his old gods, by name, in public — before he was received. Entry meant putting away the gods at the door, which is Jacob's command made into a rite.
The government form removed the border in three steps. First, entry became advantageous — the emperor's religion, the path of favor. Then entry became compulsory — profession required by law, and eventually whole peoples baptized by treaty and at swordpoint. And under that flood, the border collapsed: the years of instruction shrank toward nothing, because you can't catechize an empire. The renunciation remained as words; the thing it enacted was gone.
So the annexed populations did what annexed populations had done since Jacob's tents. They came in with the baggage.
We can watch it in the sources. Augustine's own mother, newly arrived in Milan, went to the shrines of the martyrs with baskets of bread and wine — the old funeral offerings to the dead, carried straight into the church — and was stopped at the door because the bishop had banned the practice. A convert generation, bringing the old religion's furniture into the new religion's rooms.
Two centuries later it was policy. Pope Gregory, instructing the mission to the English, directed that the idol temples not be destroyed but converted, and that the ox-sacrifice feasts continue, redirected to the martyrs' days — because a rude people couldn't be cut off from everything at once. Read it with charity: it was pastorally intelligent. Read it with clear eyes: it was a written policy of scaling by retention. Keep the places, keep the feasts, change the names. It was the Samaria settlement administered from the church's side.
Why distance from God grew as the numbers did
Three reasons, and they compound.
First: formation is relational, and relational capacity is bounded. A person is discipled by people who know him, at a table, over years. That doesn't scale by decree. When the government form added populations by the province, it multiplied members without multiplying disciplers. The average member's exposure to formation fell toward zero while his membership was never more secure.
Second: annexation removes the renunciation. Multiplication carries the border with it — every new household can ask its entrants what they're putting away. Annexation has no door to stand at. When everyone inside the border is a member by law, there's no moment at which the old gods are named and left. So they aren't left. They're brought.
Third: universal profession destroys the signal. When everyone is called Christian, the word no longer distinguishes the formed from the unformed — which means the imported gods become invisible. In Samaria the historian could still see both religions and name them in one sentence. In Christendom the two wore one uniform, and the old allegiances went where Ezekiel said idols go when they can no longer stand in the open:
Son of man, these men have set up their idols in their heart. (Ezekiel 14:3)
Inward. Into honour, wealth, power, kin-loyalty. Where a uniform outward religion hides them perfectly. And eventually the church was no longer hosting the foreign gods. It was teaching them.
The test for any era
The principle didn't retire with the emperors. Whenever the church gains people faster than it can form them — by law, by fashion, by a movement, by a platform, by a political alliance — ask one question: what did the newcomers renounce at the door?
If the answer is nothing, then the gods came in with them. It isn't because the newcomers were insincere — the Samaritans feared the LORD, and Monica loved the martyrs — but because nobody stood at a door and asked, and unrenounced gods don't evaporate. They acclimatize.
The design scales like a living thing exactly to keep the door. Every multiplied household is small enough to know its entrants, ask Jacob's question, and hear Joshua's answer. That isn't an inefficiency. It's the customs house — and every form that scaled faster than it could form has smuggled a pantheon, called the cargo Christian, and worshipped it in good conscience for centuries.