Ephesian elders and the Jerusalem church
Now, consider Paul’s speech to the elders at Ephesus –
(Act 20:17-21 NAS) 17 From Miletus he sent to Ephesus and called to him the elders of the church. 18 And when they had come to him, he said to them, “You yourselves know, from the first day that I set foot in Asia, how I was with you the whole time, 19 serving the Lord with all humility and with tears and with trials which came upon me through the plots of the Jews; 20 how I did not shrink from declaring to you anything that was profitable, and teaching you publicly and from house to house, 21 solemnly testifying to both Jews and Greeks of repentance toward God and faith in our Lord Jesus Christ.
He was addressing the elders of a single “church” (v. 17). And yet Paul had taught “house to house” (v. 20). “House to house” translates kat’ oikous — “according to houses” or “distributed to houses.” The church meeting “in” a house meets kat’ oikon (according to or as distributed to a house).
A typical First Century home would hold about 10 people. The wealthy would be able to host 30 or 40. Archaeologists have found a Second Century Christian house modified to host gatherings of up to 70 or so.
The church in Ephesus was a large and prominent congregation. It surely met in more than one house! It was large enough to have a plurality of elders. Paul labored there for years. And yet it was a single church under a single eldership.
None of this should be a surprise, because it’s exactly what we read about in Acts 2. The Jerusalem church — of over 3,000 members! — met in houses but was under a single leadership of elders and apostles. They sometimes met in the temple courts — which could hold many thousands — as a single body, but they ate meals together and studied God’s word in house groups. Luke tells us about the organization of the Jerusalem church because it became the typical way of doing church throughout the Empire.
Of course, the church was quickly thrown out of the synagogues, and the Romans soon realized the church was not merely a sect of Jews. That made the church illegal and kept them from buying property as a church and from meeting in public facilities, such as an amphitheatre, absent a kind official looking the other way.
The “house church” was not, therefore, a church at all. Rather, Button and Van Rensburg conclude,
Lexical studies show that the formula H KAT’ OIKON EKKLHSIA [ē kat’ oikon ekklēsia]  does not refer to a self-contained unit called “church” within the local church of the city. Rather, the formula refers to a group which is part of the local church, which derives its identity from the local church and is an expression of the life of the local church.
The New Testament “pattern” is a single church in a given city, which meets in multiple houses but which is under a single eldership. The whole church would assemble together as the law, officials, and space would permit.
There is more evidence for this conclusion. Churches were led by a group of men called “elders.” In the Old Testament, we find that the elders were the governors of each city and town, serving as judges and the city council. They even decided who could enter through the city gates. It was unimaginable that there would be multiple, rival groups of elders in the same city.
We know from the New Testament and history that Jerusalem was still governed by elders (Acts 4:1), despite being subject to the oversight of the Romans. Jewish synagogues were ruled by elders (Matt 15:2; 16:21; 21:23).
In Christianity, churches were led by elders. Why borrow the term “elders” from Judaism unless the position had something in common with Jewish elders, who led on a city-wide basis?
Church elders were leaders of the church of the city. Remember, Christians thought of their Christianity as an ethnicity or nationality.
Under Rome, elders became rulers of synagogues and continued to have civil authority over the Jews to the extent allowed by Rome. And there was normally but one synagogue in a city. Even in Jerusalem, where there were multiple synagogue buildings (the Jews there couldn’t physically fit in just one!), the elders still governed as a single body –
(Mat 26:3-4 ESV) 3 Then the chief priests and the elders of the people gathered in the palace of the high priest, whose name was Caiaphas, 4 and plotted together in order to arrest Jesus by stealth and kill him.
(Mat 27:1 ESV) When morning came, all the chief priests and the elders of the people took counsel against Jesus to put him to death.
(Act 4:5-6 ESV) 5 On the next day their rulers and elders and scribes gathered together in Jerusalem, 6 with Annas the high priest and Caiaphas and John and Alexander, and all who were of the high-priestly family.
Therefore, we are hardly surprised to find that in Ephesus there was but one eldership, even though overseeing gatherings in multiple houses, constituting but a single “church.”
 NT Greek has two letters for e — eta (η) and epsilon (ε)– and two letters for o — omega (ο) and omicron (ω). To use a standard keyboard to communicate these distinctions, Greek scholars often use w for omega and h for eta — the English letters looking similar to the Greek letters. This is, of course, very confusing for everyone else.
(Many also prefer to use all caps, because lower-case letters were not invented until centuries after the apostolic age.)
I prefer to indicate eta and omicron with an English long-e or long-o, which is how some people pronounce those letters in Greek, although there are multiple schools of thoughts on that. And it works for the Greek scholars, too. But sometimes I don’t bother because it’s a pain in the neck to find and type those characters in HTML.