Pastors are also known as shepherds or to say the least co-shepherds with Jesus being the Great Shepherd. and the people are to be part of that flock, which would be under the shepherd. and also we break down the Local assembly as One body having many members, but one Body as well as the Big Church being the Body of Christ, with many members but one Body, but with one Head as well as the local assembly needs to have one head, as long as that head is in line with scriptures. now I wouldn't won't anyone to join a church for this reason but if you decide not to join a church and ten years later someone at your work joins the same church you are attending and both of you loses your jobs, then the Church should help the member first over you, even though you have been going there the longest.
But Bibical I see church membership in alot of areas in the Bible but no there is no verse that says ye must join a Church. if two people from the Church say one is a member and the other is not. and let's say that the one that is not, does something against the member and the member tries to apply Church discipline, where they go through the steps with the last step being before the Church, and the Church agrees that the non member wronged the member and they apply church discipline then the non member doesn't have to apply, to the finding of the church simply by saying I am not a member here I don't have to do what you all say. and I think this is where being part of the flock comes in the play. plus the member of the Church are suppose to receive spiritual gifts to edify the Church, if you are not part of the Church, then God may not bless you with gifts, if you are just in it for yourself and not what you can give back to the local assembly. we have a saying here I twisted the words of a Pres, Kenndy. Ask not what the church can do for you, but rather ask what you can do for the Church and this should be the goal of every member. if you never joined i think that would be a very selfish act, because you would never be able to use what God has blessed you with, to help out others.