Although we cannot know for certain the particular motivations of every explorer, historians do generally say that there were three kinds of motives that drove Europeans to explore. These are often listed as “god, gold, and glory.” There is no way to know which of these motives was strongest for any particular explorer.
“God” refers to the idea that explorers were motivated in part by their religion. Some explorers felt that it was their duty as Christians to bring the word of God to people who had not yet been exposed to it. Therefore, they explored out of a desire to (in their minds) save souls.
“Gold” refers to the idea that explorers were motivated in party by the desire for wealth. We can see this, for example, with Christopher Columbus. The point of his expedition was to find a direct sea route to Asia. This would have brought riches to him because it would have made him the first to find a faster route to and from the places where Europeans bought spices. Explorers like Hernan Cortes became rich through conquest. In other words, explorers were interested, in part, in getting rich.
Finally, “glory” refers to the idea that explorers were motivated by the desire to become famous. We know that adventurers in our own time are attracted to becoming the first to scale a certain peak, or the first to accomplish a certain voyage. The idea behind “glory” is that explorers in the past wanted this kind of fame and glory as well.
Thus, there are at least three major types of motivations that played into the attitudes of the European explorers.