Numbers are important in the Bible. I wouldn't go as far as saying there are codes and we can somehow interpret everything from who we are going to marry to what time we are going to take a #2 in the bathroom, as some people do (I'm looking at you Michael Drosnin--but if you truly believe what your book teaches, then you probably already know that.).
So how do I mean they are important? Often God uses them symbolically in the Bible. 40 is one such example. Jesus was tempted for 40 days. What else happened in the Bible with the number 40? It rained for 40 days and 40 nights, and Noah's faith was tested; children of Israel also wandered around for 40 years with Moses; Ezekiel lay on his right side for 40 days. What's the commonality there? Why is it symbolic? In each instance it's really a period of maturity--I wouldn't call it testing as much as preparing.
And how about the 12 disciples? What's so important about the number 12? 12 comes up a lot when your talking about government in the Bible; there are 12 tribes of Israel. The temple of Solomon has the number 12 referenced too a lot; and in revelation there are 12 foundations, 12 gates, 12 pearls, 12 angels. It's actually referenced to a lot more in Revelations. So why 12 disciples, I believe it has more to do with the 12 tribes than anything else; in the Old covenant there were 12 tribes, in the New covenant there were 12 disciples--but are essentially the foundation of God's people.
If you want to know more about Numbers, check out a book on "Biblical Numerology."