(An extra one prior to one about Greenbelt, in response to comments)
Sam's first rule of worship: worship is useless, and as soon as worship is used for something else, it ceases to be worship.
In other words, worship must be centred upon God with all our heart, mind, soul and strength. As soon as we say 'let's do worship this way, in order to achieve X' (where X is anything other than 'worship God more effectively') then we are no longer loving God with all that we have. We have allowed another priority to intrude, we have slipped our moorings and begun to drift with the tides.
- Mission and evangelism. Where a service is geared around bringing people to faith through what is expressed and achieved in a service, then worship is compromised. That is not to say that people don't come to faith through worship - clearly they do. Nor is it to say that we should take no account of how people experience worship when planning services - clearly we must but that is because we must be concerned with what will enable people to worship. There is an ultimate difference between asking 'what will enable people to worship' and 'what will enable people to come to faith'. The former is legitimate (and might achieve the latter); the latter is, in the end, an abandonment of worship. When the Reformers introduced worship in the vernacular, that was something that enabled worship. It probably also enabled a deeper conversion in people, and was missionary and evangelistic, but those were the healthy byproducts, not the main outcome sought.
- performance (especially in music but also in sermons, sometimes also in the intercessions). When the pursuit of excellence in musical performance becomes an end in itself, and has become separated from the spiritual activity of the community as a whole, then worship is compromised. The achievements might be immense, the music might be breathtakingly beautiful or stimulating, but where the spirit isn't right then worship is no longer present. God is much more honoured by something imperfect but sincere and heartfelt than by something highly polished and accomplished that is oriented away from Him. This is not to say 'don't pursue excellence' - OBVIOUSLY we pursue excellence - but we pursue excellence within the larger framework that in the end all we can offer to God is dross. 'Only by grace can we enter...' and all that.
- liturgical correctness and formality. When those involved in all the formal elements of a service have become excessively focussed on doing things 'correctly' then worship is compromised. Yes, all things must be done decently and in good order but church is not a military operation and it is most essentially a human endeavour. So insisting on perfect right-angle turns, inhibiting any human contact eg between priest and servers (or between priest and people), insisting that those serving must wear highly polished black shoes (and being scandalised if a young server happens to be wearing trainers) - these all risk missing the point.
- political correctness. I have often worried about whether it was right for me to criticise Tesco in a sermon, not because I don't think what I said was true but because it didn't leave much room for people to disagree. Perhaps I am wrong. I do think that it is legitimate for Christians in general, and clergy in particular, to be politically engaged, so long as they are not party-political, eg saying 'Vote Labour' or 'Vote Conservative' from the pulpit but the danger with becoming too specific with political points is that it overwhelms the worship. What is the difference between a service of worship and a political rally? Allowing God to be God, and acknowledging and praising God for being God - which means accepting things like: we are all sinners, we must not stand in condemnation against other people, we must not think that our actions are the most important actions, which lead to the equal temptations of giving in to despair or an excess of hubris. There is a clear Scriptural mandate to be politically controversial in terms of Christian life and witness; I am not clear how far it is legitimate to be specifically controversial in Christian worship. Preach and sing about God's bias to the poor, yes, but saying that the tax rate should be raised to 50%? Probably not.
I'm sure there are other ways in which the priority of worship can be distorted, and the power of worship prostituted to human will. Worship is useless, and must remain useless, it is a divine waste of time.
Other posts in this series:
What makes worship distinctively Christian
Participation and Performance