1. why did britain want an empire?
2. why did the 'sun never set' on the british empire?

Britain sought to build an Empire because at the time it was seeking to dominate the European Continent and the world in terms of its military and economic power. It was believed at the time that a vital piece of international power was the control over colonial territories to increase the wealth, power, influence, and prestige of a nation. The phrase the "sun never set on the British Empire" was used to describe the fact that the British Empire was so extensive that at any given time of the day the sun was always shining on a portion of the empire. 

That's true, it's a belief in one god