Why is primary sector important to a country's economy?

Why is primary sector important to a country's economy?
The sector of an economy making direct use of natural resources. This includes agriculture, forestry and fishing, mining, and extraction of oil and gas. This is contrasted with the secondary sector, producing manufactures and other processed goods, and the tertiary sector, producing services. The primary sector is usually most important in less developed countries, and typically less important in industrial countries.