Now that we can see that scriptures use of the word Ekklesia by itself lets us see who the church is made up of it is the context of scripture that helps see more of what the church is. One the first areas that is dealt with is the nature of the church as it relates to the local/visible church and the universal/Invisible church.
As you read about the church you will see that many people tend to take up the cause of one side or the other so as to often times promote their view of what the church should be. One example with regards to the Local Church would be the Roman Catholics and even Landmark Baptists (you probably do not see these together often). Both of these groups focus on the local/visible church so as to promote the idea that the church is an organization and thus has some jurisdiction or say over other churches that would be part of this organization. An example of those that would promote the idea of the Universal/invisible church would be the Plymouth Brethren that do not see the church as an organization but an organism and thus have noo church membership (at least in paper form) and no ordained clergy .
Which side is right or are both wrong? As I read scripture it would seem clear that both exist. For example the scripture we have comes to us in many forms but one of those is that of letters to specific churches and even if you see some of the letters being circular letters to a number of churches it would speak to the existence of the local church. The word Ekklesia which we previously saw as “called out ones” also refers to an assembly and was often used in Greek to refer to such groups so there is in the word itself the idea of both universality in the nature and locality in function.
Thus I think the clear teaching of scripture is that the Ekklesia is made up of all believers in the world that also shows itself in gathering locally. Notice that none of this speaks to how they gather or where but more to the who of the church. The issue that all too often muddies the water is that the word church is often seen as more of an it than a who and this does not give a clear picture of what God has called the church to be.
When a group such as the Roman Catholics, or Landmark Baptists, claim that the local church is all there is and they are it, this then says that if you are not in their church you are not in THE church, as I think Vatican 1 speaks to. Before one jumps on the wrong bandwagon many protestant or evangelical denominations have issues of their own. The issue is that the meaning of the church or Ekklesia is missed and the concept of a regenerate membership seems to be lost. If we truly saw the church as for the “called out ones” we would seek to not have those that are not yet believers, this includes children and infants, as members. What it would, or at least should do, is refocus our attention on what the church is to do and that is to worship God and not seek to placate the world or make it comfortable. This does not mean we ignore unbelievers but it says we are to focus our attention on leading believers into correct worship of God, since unbelievers cannot worship Him. We are not to take cues from the world as how to do this but from scripture.
What I hope I have answered, or at least perked interest in, is that the church is much bigger than any one local body but it is made up of many such bodies and the idea of a Universal/Invisible church allows us to have a fellowship with other believers worldwide and should enhance not only our desire for missions but for aiding other churches. Worldwide. This is similar to what Paul did in collecting for the Jerusalem Church to aid it in its poverty. I would pray that we do not lose focus on the local/visible church and that we do not neglect the universal/invisible church but seek to promote both.
Added 8/3/06:
One becomes a member of the Universal/Invisible church as soon as conversion takes place. Thus they become a part of the “called out ones” as a whole. However, since we are called to live the “called out” life in a community of other believes, the assembly side of Ekklesia, once one is a believer they need to find a place to use the gifts that come with conversion and join an assembly. From this we see that both concepts are important and need to be viewed as such.