What are reasons for Spain to explore and colonize America?

For God,gold, and glory....Spreading the religion, searching for spices, and conquering the country to gain more power..

New terrritories and the lure of fantastic tales of the city of Cibola (the streets of which were said to be paved in gold) as well as the tales of the fabled land of Califa, present day California...

The three "G's" Gold, Glory, and God. Colonizing America spread the Christian faith and increased the prestige of Spain. And there was the lure of gold too, which was a powerful motivation.

Spain colonized the western United States east to Florida, Mexico, and most of Central and South America.

The reason they colonized is because they wanted land in the new world. They saw that the Spanish were getting rich from the land and the animal in the new world. They saw a chance to do the same.