What motivated English colonization of North America?

It depends on which particular settlement you're referring to. The Jamestown settlement, for example, was primarily a commercial venture. The Virginia Company saw the new colony they established (Jamestown) as an opportunity to generate considerable wealth. Young Englishmen were lured to Jamestown by the prospect of riches, which they hoped would allow them to return home with the wherewithal to lead lives as respectable gentlemen. Jamestown was looked at, then, as a means to an end; it was a short-term project designed to exploit the native natural resources for all they were worth.
Later colonies, such as Plymouth, were established on rather different grounds. In seventeenth-century England, official religious persecution by the authorities led many Protestant dissenters to feel that they needed to seek a new land where they could freely exercise their religion in peace. Because of its very nature, this was a long-term project. And so the Pilgrim Fathers sought to establish a godly kingdom which would endure, acting as an inspiration for countless other Protestant dissenters looking for a haven from intolerance and persecution.