The main motivator for Christopher Columbus was to find a cheap route to the source of spices. Spices were a lucrative trade during Columbus' day. Before the days of refrigeration, food spoiled easily. If you were wealthy enough to afford flavorful spices, you could enjoy better tasting food. Spices, such as cloves, allspice, vanilla, and pepper were well sought after by the elite of Europe. However, they came from far away in South and East Asia. Throughout the middle ages, overland trade was the only way that these spices reached Europe. This trade was mostly dominated by Arab merchants and would pass through many middlemen, meaning that they were very costly by the time they reached European markets. Colombus sought a sea route directly to the source of these spices. He believed that by sailing west he could find a way directly there that would also bypass the routes recently established by the Portuguese who were sailing south and east around Africa.
To a lesser but still notable extent, Columbus hoped to spread Christianity, particularly Catholicism, to the lands he reached. Queen Isabella of Spain, Columbus' sponsor, was an ardent Catholic. She hoped that Columbus would carry the religion with him and convert the people he met in the East to this faith. To that end, Columbus promised the queen that he would be an evangelist of Catholicism in new lands.
We must also consider Columbus' ego as a reason he was looking for a new sea route to Asia. Simply reading his journals shows that he had a large sense of self-aggrandizement. It is clear that he saw himself as destined to be one of history's great figures. He even felt himself to be chosen by God to change the world. This might lend some insight into why he refused to give up when he was repeatedly rejected by potential sponsors until he was able to convince the Spanish monarchs to support his voyage.
Further Reading
Columbus, along with his sponsors Ferdinand and Isabella of Spain, knew that the name of the game for acquiring vast wealth was finding a new route to Asia. The Ottoman Empire had made both overland or Mediterranean Sea crossings expensive and dangerous, so Europeans were searching for alternatives. They felt they couldn't live without the spices and other goods Asian countries provided.
The Portuguese had already found a route around the tip of Africa and were becoming very rich as a consequence. Columbus and his sponsors wanted a piece of that action.
Columbus thought he could reach India by sailing west across the Atlantic. He never anticipated bumping into a new continent. His goals were to bring back goods that would make Ferdinand and Isabella wealthy, to amass a fortune himself, to become famous, and ostensibly, to spread Roman Catholicism. The latter goal was not primary but more an acceptable way to justify making a voyage that was for the purpose of accumulating wealth. Columbus never reached India, but he did find much to plunder.
Despite being most famous for finding the Americas, Christopher Columbus's first voyage in 1492 was actually funded, by the rulers of Spain, as an attempt to find a new trading route between Spain and Asia. The first reason Columbus undertook this voyage, was because he believed that by traveling east over the ocean, rather than west by land, he would be able to reach Asia in much faster and safer manner than the traditional route, or the newer route, discovered by the Portuguese, which included sailing all the way around Africa. The problem with this thought was two-fold, first Columbus did not know he would run into another continent between Europe and Asia, and second, he grossly underestimated the circumference of the earth, causing him to miscalculate how long the journey would take. His second reason for embarking on the voyage was one of wanting personal wealth and fame. He thought that by discovering this new trade route, and also being privileged by the King and Queen of Spain to 10% of all the riches he found, as well as all the land he found, he would be able to achieve this. Finally, his third reason for embarking on the voyage was to spread Catholicism from Europe to Asia, and the rest of the world, an idea that both Columbus and the King and Queen of Spain thought was important at the time. Hope this helps!
Further Reading