Churches are never commanded to be accountable to "Caesar", in today's case that would be the Federal/State and local government and/or the IRS.
The commandment to start indigenous, visible local churches comes from a divine mandate from the Lord himself and the rules thereof are clearly detailed in Scripture, NOT IRS publications or corporate laws. There are so many that churches seek the advice of LAWYERS to "set-up" their corporate churches. Primarily to ensure they are a "legal charity".
A 501C3 church disqualifies as a NT church because it is now a "legal fiction" and is under the authority of the government and the IRS.
An unincorporated church has as its head the Lord Jesus, is accountable to the membership and NOT the IRS/government, its SOLE source of practice is the BIBLE and not mans laws/rules/statutes/codes. In short Christ is the leader. I believe in Christian responsibility and accountability to Jesus, his Word and to the brethren (including church leadership), not responsibility and accountability to IRS code and mans laws. I say this in context as a New Testament church as a BODY. Individually in society, sure be law abiding. Taxes are paid by citizens NOT the Lord's Church.
As to the definition of a church - well that is found in Scripture NOT IRS codes, publications and corporate law. Since a New Testament Church doesn't file "official documents" with Caesar or the IRS I fail to see how a New Testament Church could be taxed. If you file for "legal tax exempt status" you are no longer a New Testament church you have now displaced Jesus as Lord over his church and placed in his stead the IRS and Caesar and now MUST follow THEIR rules.
Though the church is made up of people and people are subject to society's laws the FUNCTION and the administration of the Lord's Church is NOT subject to those laws. The Lords Church can not have two masters.
What is God's - His Blood bought Church - is NOT Caesar's unless of course you give it to Caesar by registering with him and seeking his approval. The New Testament local church is NOT Caesar's, but Johnv believes it can be, the martyr's of the past say NO!! No King but King Jesus.
I never said that NT Churches are not subject to the laws of man; they are NOT under the jurisdiction of man's laws. Sure since the formation of the local visible church, man has tried to control the TRUTH and the blood of martyr's is the proof.
Johnv let me ask you is it "right" for missionaries to start "under ground" churches in countries where "Caesar" has outlawed the Gospel and Christian churches? Or how about where a country says to be "legal" you can do that but can't do this. How much authority does "Caesar" have over the Lord's Church? Who is the church accountable to, Caesar or Jesus? You can't have 2 masters there Johnny.
Churches are accountable to the membership. Those in leadership be it an elder run church, or pastor(s), or trustees or deacon/pastor or whatever, they ARE accountable to the membership as a body not any outside government entity. Churches are certainly free to have their books audited by a CPA for example, if done so voluntarily and with approval of the membership but to abide by IRS mandates - forget it, its unbiblical to place ANYONE or ANYTHING over the Lord's Church.
Believers should make sure they are giving to a Bible based, New Testament Church, not whether if it's a "proper 501C3 charity" approved by the IRS as such.
I have provided links and numerous ways a 501C3 not for profit incorporated church is not a New Testament local church. Primarily because there are unbiblical rules, mandates, laws, codes and statutes that an IRS approved 501C3 not for profit corporation must comply with. These laws are becoming more controlling each and every year and are NOT based on the Bible.