J.I. Packer has written a work in answer of the question “If God is sovereign – if He controls everything, then why should we tell people about Jesus?”. What is the difference between the precepts of God (what God wants from our behaviour) and the purpose of God (the plans: the things that will definitely happen). If you’ve pondered this, it’s a book that will make a rewarding read. (Hint: we evangelise because God tells us that we should).