There's an oft-quoted phrase of Rick Warren's: "There's no such thing as Christian music, only Christian words." It's become a catchphrase, and in the context in which he brings this up in the book, I don't disagree. There is no single style of music that can be called 'Christian'. Some like hymns, some like psalms, some like 1980s worship music, some like 1990s Vineyard music, some like Taizé music... all can be used to worship God. To suggest that we can only worship God by singing Psalms, or - at the other extreme - that we should reject all music written before the 21st century as out-of-date - is unbalanced. God loves variety, and has created people with huge diversity of musical tastes and talents. So by all means, let's worship him in many ways: with all styles of music, and in other ways. Warren's point about worship being a lifestyle is also valid, of course.
But... 'Only Christian words'. What does he mean by that? The implication is that if a song contains Christian concepts, then it's a Christian song and can be used for worshipping God. If it doesn't, then it can't.
Is that the case? Many would disagree. Amongst the songs to be found in most current Christian songbooks, there are some which are clearly worshipful, some which state theology rather than expressing any kind of worship, and some which are trite in the extreme. Merely because a song mentions God, and is written by a Christian, does not mean it's going to be worshipful. I think of Adrian Plass's fictional diaries... someone wrote out the most appalling pseudo-Christian doggerel and insisted God had given them the song. Plass's wry comment was that God was probably glad to get rid of it. Is God worshipped by 'vain repetition' of religious phrases? Or, indeed, by the heavy and rather severe theology of some of the old hymns?
I don't say that he can't be. God enjoys our worship however it's expressed, and I'm sure that even the tritest (or heaviest) of songs can be song with a reverential and worshipful heart. But they can also be sung by people who think they're dreadful, or boring. When I was a teenager, visiting a rather dull church, I noticed the word 'assuage' in a hymn we were singing, and spotted that it's an anagram of 'sausage'. I tried in vain to suppress the giggles, which ensured my rendition was far from worshipful.
Then there's the other side: music without words can undoubtedly be worshipful. A musician playing a clarinet, or a trumpet, cannot sing the words at the same time, but can certainly give worship while playing, either alone or as part of a church service. If worship is showing God's worth (as the word means) and expressing our love, then the words as such are almost irrelevant. What matters is our heart and our attitude.