A combination of the motives you described.

In Europe, during both the first colonial era, with the colonization of the Americas, and the second colonial era, with the colonization of Africa and the Middle East, countries were competing with each other for prestige, resources, and strategic territory.

On the prestige side, having colonies was a must if you wanted to create a powerful empire. For instance, this is why the German Empire was so set on having African colonies, as colonies were a matter of prestige, as well as practicality. Its also why Italy's inability to conquer and colonize Abyssinia(Ethiopia), was so shameful.

Colonies were also a highly practical matter. The resources from colonies, particularly those in Africa, fueled the industrial revolution of the late 1800s. Resources like rubber in the Congo, Copper in Zambia and South Africa, and tin, were all necessary products to create the products and machinery of the industrial revolution.

Colonies also served a strategic purpose. Many were chosen for their position, which would allow them to be used as refueling stations for naval vessels. The Suez Canal, while Egypt was under British control, served both a commercial and strategic use. It allowed faster transport of goods, while also allowing a quicker route to India to put down rebellions or threats to their control.

Ideas of religious or racial superiority certainly played a role. The US decision to annex the Philippines was attributed to the duty of America as a "civilized" and "christian" nation to convert and modernize the natives (even though the Philippines, having been a Spanish colony for centuries, was heavily Catholic). However, while some legitimately believed in these causes, these beliefs served as a convenient cover to gain the resource and strategic benefits of colonies, under a selfless stated goal.