Ancient Greece rose out of the earliest cultures of Europe around the shores and islands of the Aegean Sea. Long before Homer, ancestor worship made family ties very strong and after that the families came together to form tribes and then villages. Villages joined to form the polis, city, from which our word "politics" comes. The government of these Greek city states was called ekklesia, assembly, the town meeting. The first known assembly was held as early as the reign of Draco in 621 B.C. At each meeting of the assembly certain topics were discussed and voted on. The assembly would also gather in cases of emergency and in cases of trials of law in which the assembly became a jury. Votes were taken by a tally of hands raised. After being tallied the majority decision ruled and carried.
Throughout the Greek world right down to New Testament times (see Acts 19:39), ekklesia was the designation of the whole body of citizens in a free city-state, "called out of" (ek--out of, klesia--called) their homes by the kerux, the herald, for the discussion and decision of public business. Translators of the Hebrew Old Testament used ekklesia to render the Hebrew qahal, which means "congregation." We see Stephen in Acts 7:38 call the Old Testament congregation of Israel the "ekklesia in the wilderness."
Jesus thought the same about ekklesia. Ekklesia occurs only twice in the gospels. It is clear from the second usage in Matthew 18:15-20 that Jesus had in mind an almost identical meaning to the historic usage of the word. He used ekklesia like the people hearing him in that day would have understood the word. It was a congregation possessing powers of self-government in which questions of discipline were to be decided by the collective judgment of members.
The only other times after Matthew 18 that we see Jesus speak of the ekklesia are the nineteen occasions in Revelation 1-3 in which in each case is a distinctly local, functioning, and organized assembly of people. Those attempting to discern a definition of ekklesia based on His usage of the word would see it as something like the governments of the ancient Greek city states. The major differentiating factor was that these assemblies to which He referred were His assemblies, now sacred not secular. In Matthew 16:18, Jesus said that that He would build "my assembly" differentiating it from the then congregation of Israel and the secular Greek town meeting.
If I said that Greek cities operated with the government of the city-state, no one would assume that there was only one. They would assume that each city had its own town meeting. When Jesus said He would build up (oikodomeo, "edify") His ekklesia, we should not assume that He meant that there was or would be only one in number either. His ekklesia would be how the Lord Jesus Christ would operate on earth until He left and after He was gone.
Hebrews 2:12 accounts for the ekklesia of Jesus functioning while He was still on earth and not yet ascended into heaven, when it says: "Saying, I will declare thy name unto my brethren, in the midst of the church will I sing praise unto thee." Jesus sang in the ekklesia. He could not have done that if His ekklesia had not yet started. He was not standing in the midst of every believer on earth.
When the Lord Jesus incorporated the term ekklesia, He took a word with distinctly local and visible connotation. He sanctified it for His own use, but He did not give it a whole different meaning. The word excludes anything broader than a meeting or gathering. The concept of universal or global contradicts the meaning of the word. If Jesus wanted His governing institution on earth to have some larger context than local, he could have used "kingdom" or "family" or "nation" or "empire" or "state." But He didn't. He used ekklesia.
In both 1 Corinthians 1:2 and 2 Corinthians 1:1, Paul writes: "unto the church of God which is at Corinth." To make the ekklesia something more than local only deviates from the meaning of the word. An ekklesia must be at some local context---city, town, village, area. All believers did not reside in the city of Corinth. Paul wrote to the church at Colossae and he told that church to pass that letter along to the church of the Laodiceans, seeing that those were two separate churches (Colossians 4:16). Paul wrote to the church of the Thessalonians (1 & 2 Thessalonians 1:1). He said that the bishop, the pastor, is to "take care of the church of God" (1 Timothy 3:5). One man isn't responsible to take care of all believers on earth. At the end of 2 Timothy, the afterwords say that Timothy, to whom 1 Timothy 3:5 was written, was "ordained the first bishop of the church of the Ephesians."
A church is local only because that is what ekklesia, the word translated "church," means. I'm not trotting out landmarkism or Baptist bride-ism. Those who make ekklesia anything other than local only are reading something into the word that isn't there. It never has been.