Because they are an insurance company, their reported earnings and change in book value will often not match. That is because only the profit or loss from investments which are sold count in earnings whereas the change in value of investments is included for the most part in book value. A life insurance company like NWLI will only sell a small percentage of their assets in a year, so this can vary greatly.
Watch the CNBC interview with Warren Buffet from a couple of weeks ago. He came out and said he could make his profit be what ever he wanted it to be based on the timing of asset sales. That is why change in book value, which Warren Buffet emphasizes, is often a better measure for the success of an insurance company.