How did religious beliefs cause Dutch immigrants to aggressively expand their settlements?

The early Dutch settlers settled in Cape Town in 1652. They built the town, the first permanent European settlement in Africa, in order to supply ships that were passing by on their way to East Indies. Boers, or Dutch Farmers, settled in the vicinity of the town and began ousting, killing and enslaving the people who lived there. They held a belief that they were chosen by God and viewed Africans as inferior, By the 1700s they had started moving north and began battling powerful African clans like the Zulu's.