Religion and Art together

I was wondering to what extent religion and art go together.  How far do they go hand in hand?  Is there a point to which they are the same thing?  van der Leeuw says that religion and are are so close together that they can be equated to be the same thing.  "Song was prayer; drama was divine performance; dance was cult."  (Page 11) He thinks that they can be the same thing art and religion.  However, if they are equated to be the same thing, what then makes them different?  Why don't we just classify them to be one thing?