Ernst Troeltsch was born in 1865 and died in 1923. He was a German Protestant theologian, and one of the things he wrote about was the difference between Churches and Sects – two different expressions of Christianity, which distinction is still used a lot in sociology today. Don't be too put off by the names of the two 'types' – sects aren't necessarily crazy brainwashing groups. I found his discussion interesting because to me it seemed to illuminate quite clearly some of the distinctions between the charismatic/evangelical/non-denominational/house churches I grew up in and other more 'institutional' churches. If I'm right, I think you could make the case that there's a good dose of crazy on both sides, though perhaps Troeltsch can help us think about the variety of crazies on offer within Christianity as a whole.
Troeltsch says that churches are conservative – they accept the relationship between Church and state as it is, and see themselves, in principle at least, as universal, able to include the whole of humanity under their wings. They base themselves on the 'objective concrete holiness' of the priesthood, the Apostolic succession and the sacraments. They tend to be intertwangled with the State and the 'ruling classes' – they feed off each other, and so the Church becomes part of the social order.
The essence of the Church 'type' is that it's institutional. Individuals are born into it, and the institutions of the priesthood and the ecclesiastical hierarchy mediate grace by virtue of their place in the institution rather than their individual holiness. The Church is prepared to compromise with the world, because they see the institution as remaining holy in spite of individual inadequacy. The Church's main priority is to ensure that every individual comes within reach of the influence of the sacraments, which are the means of grace and this is why the Church wants to dominate society – in order to ensure universal access to the means of of grace. Churches tend to see the New Testament and early church as the starting point, which leads to a willingness to see doctrine as something which develops over time, and also to compromise.
Sects are smaller than churches, and their main aspiration is inward perfection and personal fellowship within the group. They organise themselves in small groups and don't expect any sort of dominance within society – they treat society with an attitude of indifference, tolerance or hostility. Where Churches focus on the 'objective concrete holiness' of their structures and sacraments, sects tend to focus on the moral demands of Jesus' teaching. Sects tend to exist either among the lower classes, or in other parts of society which don't get on so well with the state. They tend to be a lot more disengaged from society – they might refuse to engage with secular law, to swear to tell the truth in court, or to fight for their country. They tend to see the kingdom of God as opposed to all secular interests and institutions.
Characteristic features of sects include an emphasis on lay Christianity (i.e., no ordination), an emphasis on personal ethical behaviour, brotherly love, direct and personal relationship with God, criticism of 'official' theologians, and appeals to the New Testament and early Church. Sects tend to see the New Testament and early Church as a permanent ideal, which can lead to radicalism and rather literal obedience. This is partly why they struggle to become big organisations, and also why they need to constantly renew their ideal, why they tend to show a lack of continuity, a pronounced individualism, and an affinity with oppressed groups within society where 'an ardent desire for improvement of their lot goes hand in hand with a complete ignorance of the complicated conditions of life.'
All of this means that Christian life within sects tends to be very intense, but lacking in a sense of universalism as they can't help but see the wider church as degenerate. They tend to have low expectations of the possibility of changing the world through human effort, so often emphasise eschatology. Sects are also big on voluntary membership, and see spiritual progress as dependent not on the impartation of grace through the sacraments but on individual personal effort.
Troeltsch argues that these are two distinct types of church, although in real life there might be some overlap. He thinks that they're both valid expressions of important strands within Christianity, both with their strengths and weaknesses. He's been critiqued a fair bit, though I get the impression that sociologists of religion still use some version of his distinction. There's also some interesting stuff out there about the process by which sects can sometimes move towards the church type. What fascinates me is the way that I see both types expressed in some of the churches I've encountered, and I think it raises all sorts of interesting questions about churches' unacknowledged theological assumptions.