1. Is it in the Bible?
Yes. (but all uses of the word are found in the old testament, except for one use in Acts 13:43--the Greek refers to the Jewish syagogue--so the Bible is consistent with itself!)
2. What do we believe it means?
The congregation is the majority of Christians within the church who are non-ministers. It is their job to support the ministry, largely financially.
3. What does it really mean?
The Bible references tot he word "congregation" ought to give away this one! Yet again this is a reference which comes solely from the old testament--and exposes the fact that common church operation and ministerial function comes largely from old covenant "types".
In the old covenant, most of the references to "congregation" are speaking of the assembling of the non-Levitical tribes of Israel. According to the government of the old testament, only the tribe of Levi could function in the ministry of the temple. It was the work of the other 11 tribes to support the priesthood by working in the fields and bringing in the tithe offerings. Certainly a familiar "picture" to most Christians--yet an incorrect one!
The purpose of the priesthood and the functions of the congregation--the temple--the tithes and offerings--were all to serve the purpose of cleansing of the sin of Israel. Quite obviously they did not have the offering of Jesus' blood on the cross--right? God, in His mercy, gave Israel the knowledge of sin through the commandments--but also a method to be cleansed of sin (but an imperfect, temporary method as the Bible later states). God accepted the blood and flesh of animals--the grain made into bread--as a sin payment (the amount God asked for as payment-?--"tithe" 1/10th of the increase of certain herd animals and crops)
Now we new covenant believers know that Jesus is our offering for sin. but what we seem completely unaware of is that all the sacrificial laws of the old testament are annulled. there is a new priesthood (in all believers) and therefore no designation of Christians as "non-ministers/lay people.
The concept and function of a "congregation" is clearly not in he new covenant.
The equitable concept of apostleship is.