It is, as somebody else said, important that between church and state – whatever church, whatever state – that there are clear cut bonds –"Render unto Caesar the things that are Caesar's, and unto God the things that are God's". I do not see any difficulty in including the word "God" in the preamble. Even non-religioius people can have a belief in a power greater than themselves, an Almighty. However, it may or may not happen.