Columbus was the second European to make it to the New World (Lief Erikson was the first), and the first to establish a permanent settlement there. However, anyone undertaking such a journey would have had to have excellent motives for going. Columbus was no exception. He had at least two motives to go to the new world.
The first motive to make the trip would have been to convert the people living there to Christianity. In 1492, the Spanish and most of the other Christian states were fighting the Turks. Telling other people the Gospel is significant to Christians and Columbus very likely wanted to tell the native people about Jesus. Furthermore, Spain would have gotten a useful ally in their fights with the Turks.
The second motive was for his wallet. In his eyes, the New World was likely filled with gold, and there was a big possibility for him to MAKE LOTSA BANK. Furthermore, the government that sent him were eager for the gold and the territories, over which he would be made governor.