Make a joyful noise unto the LORD, all ye lands. Serve the LORD with gladness: come before his presence with singing. Know ye that the LORD he is God: it is he that hath made us, and not we ourselves; we are his people, and the sheep of his pasture. ~ Psalm 100:1-3

The Judaizers wanted Gentile converts to be placed under the Law of Moses. Paul had much to say about this as he begins the doctrinal section of his letter.