Take a look at Acts 2 (vv.41-47), after the Holy Spirit came at the Feast of Pentecost and Peter spoke to the crowds:
Then those who gladly received his word were baptized and that day about three thousand souls were added to them. And they continued steadfastly in the apostles' doctrine and fellowship, in the breaking of bread and in prayers....Now all who believed were together, and had all things in common, and sold their possessions and goods, and divided them among all, as anyone had need. So continuing daily with one accord in the temple, and breaking bread from house to house, they ate their food with gladness and simplicity of heart, praising God and having favor with all the people. And the Lord added to the church daily those who were being saved.
The first thing they did after they came to faith was to gather together daily at the temple. It was known that believers gathered at Solomon's Portico, and they also met in each other's houses to break bread (have Holy Communion).
The story of Ananias and Sapphira (Acts 5)shows how important this is by how deadly it was when it was broken. Ananias and his wife sold their property and gave part of the proceeds to the church. Was this wrong? Of course not. What they did though, was let everyone think that what they gave was all of the proceeds. They wanted to be acclaimed for their generosity and to be held up with those who had sold their belongings in order to share with others, while really not doing so. They lied before God and man, and because they did so, they immediately dropped dead.
Then we see Paul. Paul travels all over, spending time in various places proclaiming the gospels to Jew and Gentile alike. Before he leaves, he appoints overseers for those churches, either from the men who are travelling with him (such as Timothy or Titus) or from the men who are of that flock who are believers.
Now, I know that the word "church" has different meanings. It can mean a particular building where Christians meet to worship. This in and of itself was important. They made it known, if they weren't being persecuted, where they were to be found, and often this was in the open, such as in Solomon's Portico of the Temple or in the squares of the towns. In this period of time, before and during the persecution, Christians often arranged to meet at a central spot, or in each other's homes. When I was led to go back to church, I found a church by seeing them along the streets, looking in the Yellow Pages, and learning what was being taught there. Even our denominational names can help in that. But with the abandonment of Scripture, changes in practice, and even the trying to hide the denomination through names like "The Crossing" or "community church" that is becoming much more difficult.
The church can also mean all of the believers of Christ worldwide. It is composed only of those who believe, even though in the church buildings and in the activities of the church, we recognize that there are those whose faith is dead. They are not included in this definition of church. So all who confess faith in the Triune God and who believe in Christ's death and resurrection are always members of the Church, even when they are not involved in their particular congregation.
But then there is the congregation. The congregation is a very important thing. This is shown by the fact that the first thing the Holy Spirit did after bringing people to faith is that he brought them together. Everywhere the apostles went, they proclaimed the Word, some believed, and they began gathering together. The word 'church' is used 92 times in the Bible specifically referring to a congregation of believers. (info courtesy of The Master Study Bible, Holman Press...out of print, to my chagrin).
And this is not in the context of "where two or three are gathered." There are more. When Paul writes his epistles back to the congregations he has visited, and those which he hopes to, he knows that these letters will be read there (2 Thess 5:27). If people are saying "I don't need to go, I'm just going to meet with Lycius and Petros" they will miss important things. When you look at the fact that Paul considered it this important to uplift, teach, encourage, and rebuke....they could be missing a whole lot, and straying off very easily. The church was in a dangerous time then. It still is. The gathering together, when the church is doing it's job, protects it's people from false doctrine, and proclaims the good and warns the believers who are in danger - these all flow out of the preaching of the Word and the unification that occurs in the sacramental life of the church.
Paul also points out how these churches did powerful things. When Paul was in Thessalonica, the Philippians sent aid to him. The Thessalonians in turn learned from that example. The young churches sent aid to Jerusalem when famine hit. Many of the churches sent their most promising young men with Paul to be trained, to support him, and even to help pastor new churches in various places.
But reading the epistles, it also becomes very clear that the gathering of believers around Word and Sacrament is good by what is NOT said. Paul never, EVER, specifically says "if things are not going well, go find a few friends and gather on your own" or "continue studying privately." Instead, he says:
"..but rather resolve not to put a stumbling block or a cause to fall in our brother's way." Romans 14:13b
"We then who are strong ought to bear with the scruples of the weak and not to please ourself." Romans 15:1
"Now I urge you, brethren, note those who cause divisions and offenses, contrary to the doctrine which you learned, and avoid them. For those who are such do not serve our Lord Jesus Chrst, but their own belly, and by smooth words and flattering speech deceive the hearts of the simple." (Romans 16:17-18)
"Now I plead with you, brethren, by the name of our Lord Jesus Christ that you all speak the same thing and that there be no divisions among you, but that you be perfectly joined together in the same mind and in the same judgment." (1 Cor. 1:10)
"Brethren, if a man is overtaken in any trespass, you who are spiritual restore such a one such a one in a spirit of gentleness, considering yourself lest you also be tempted. Bear one another's burdens, and so fulfill the law of Christ." Galatians 6:1-2
"let all bitterness, wrath, anger, clamor, and evil speaking be put away from you, with all malice. And be kind to one another, tenderhearted, forgiving one another, even as God in Christ forgave you." Ephesians 4:31-32
"fulfill my joy by being like-minded,having the same love, being of one accord, of one mind. Let nothing be done through selfish ambition or conceit, but in lowliness of mind let each esteem others better than himself. Let each of you look out not only for his own interests but for the interest of others." Philippians 2:3-4
"I implore Euodia and I implore Syntyche to be of the same mind in the Lord. And I urge you also, true companion, help these women who labored with me in the gospel." Philippians 4:2-3
"Therefore comfort each other and edify one another, just as you are also are doing. And we urge you, brethren, to recognize those who labor among you, and are over you in the Lord and admonish you., and to esteem them very highly in love for their works sake. Be at peace among yourselves. Now we exhort you, brethren, warn those who are unruly, comfort the fainthearted, uphold the weak, be patient with all. See that no one renders evil for evil to anyone, but always pursue what is good both for yourselves and for all. Rejoice always. Pray without ceasing. in everything give thanks; for this is the will of God in Christ Jesus for you. Do not quench the Spirit. Do not despise prophecies. Test all things; hold fast what is good. Abstain from every evil." I Thess 5:11-22
And there is so much more. But while Paul, Peter, James, and John exhort us to bear with one another's weaknesses, be loving and humble with each other, it is universally assumed and encouraged that we continue to gather together.
Unity is important. Terribly important. And even when we believe that we are completely right, unless it is a matter of doctrine, we need to look at our own attitudes and thinking and evaluate whether it is important enough to disrupt unity. When we wish to change a practice, how does it effect the life of the church? When we wish to resist a change of practice, are we simply holding to the old or are we engaging in discussion, learning the other's perspective -- or are we refusing to listen and grow before our we decide. We need to be humble and patient with those who don't see things the same way. And sometimes that means giving up when we are right, evaluating whether the cost of being right is worth whom it might hurt. When we truly believe we are right, this is a hard thing, sometimes downright painful. Being unwilling to do this has destroyed many relationships, many marriages, many congregations.
We need to overlook petty issues ("she didn't call me back" "they misprinted my announcement in the bulletin," "why is he in such a bad mood?") and lovingly allow for the sinfulness in our brethren that we would hope they would make allowances for in us(notice, that is what we are called...we are brothers and sisters in Christ..not merely friends and acquaintances. This implies that even if we tried to get rid of each other, we really aren't). When there is a serious offense, we need to go to them and talk to them in love.
This includes with our pastors. You have no idea how many times I have heard "I don't want to hurt him" because they know the pastor means well, or "I don't want to hurt the church through a confrontation" when any good pastor would much rather have you go to him and bring your complaints before him, or even reprimand him if needed, give him an opportunity to hear you, and for you to hear him....than to see you silently walk out the door. You do hurt the church when you leave silently. More than you could ever comprehend - because you are not there to see. And you do hurt the pastor when you do not bring your complaints to him. He knows something is wrong, yet you do not confide in him, whom GOD put over you to show you His love. That is wrong and it is sinful. It is refusing to acknowledge God's authority.
We are to try to find every means possible to maintain peace within our congregation, even sacrificing many of our freedoms and our rights for the sake of that unity. We cannot sacrifice doctrine, but we can try to maintain peace even through issues where we struggle with that as well. It is a big deal for a brother or sister to leave a family and not come back. We would hope that if a child chose to remove themselves from a family, it would be for a reason that was uncompromisable, and that all effort had been made by all (including the child) for them to stay - not simply because Dad told him he was wrong, or he didn't like that his sister was getting all this attention. Leaving a congregation has the same level of importance. Even more so, because we are talking about a family that God created in His name, unifying them not merely by human blood, but by the blood of His most Holy Son.
The Holy Spirit not only gives us faith, but He leads us into the body of Christ, into the congregation of believers, into the flock for our protection and our edification. Although Christ knows how many hairs each of us have on our heads and He calls us each by name, He also knows that we need each other. He works to care for us through His church.
If after there is a crucial issue with doctrine and practice, and you have tried to address it in a godly, Biblical way, you may find the need to be led to another flock. Pray about it. Do not leave in anger. Trust God to find another flock for you. But it is not in His will that you go off on your own where you are vulnerable to the wolves and to yourself. This is important for you, and for the family that God has put in your care. But in a godly way means also that they know why you left, so that if they are in the wrong, they have the opportunity to hear what they are doing, and to choose to correct it, or to choose to remain in what you believe is wrong.
This is what I have found in the Epistles. I encourage you to study them also, because there is far more there, even on the topic of the importance of the congregation, than I could ever share here.