Why was it such a big deal that christopher columbus found the “new world”

On August 3, 1492, Columbus set sail from Palos, Spain, with three small ships, the Santa Maria, the Pinta, and the Nina. On October 12, the expedition reached land, probably Watling Island in the Bahamas. Later that month, Columbus sighted Cuba, which he thought was mainland China, and in December the expedition landed on Hispaniola, which Columbus thought might be Japan. He established a small colony there with 39 of his men. The explorer returned to Spain with gold, spices, and “Indian” captives in March 1493 and was received with the highest honors by the Spanish court. He was the first European to explore the Americas since the Vikings set up colonies in Greenland and Newfoundland in the 10th century.

To the Europeans, it was basically that: a new world. It's basically the equivalent of discovering an alien planet and meting its residents. There was a lot of unexplored land which could be hiding natural resources such as oil and gold, discovering things there would win you fame and glory, and Europeans (mostly Spaniards) who saw it as their sacred duty to educate and convert others to Christianity wanted to convert the natives, which is how missions came into being. That's another story, though.

Hope this helps!