Mercantilism is the belief that power of a country is tied to the amount of wealth they have. It also states that wealth in the world is limited and to obtain the most amount of wealthy, a country must hold colonies to contribute to the "mother country".
This belief system encouraged exploration by European countries because they believed they need to get direct access to trade and obtain colonies. By engaging in mercantilism, European countries used exploration to get colonies. After getting colonies, the European country then needed to access the resources and riches of their colony to increase the power of the country.