The first primary reason for colleges, both colonial and European, was to prepare men for the ministry. Each of the early universities was tied to a specific denomination. This was to further spread their gospel and teachings of the Bible to the men that came there. Those men would, in turn, further spread the gospel after they left and took up their posts in various towns. It was also a way to codify and unify the message of the church.
Secondary, was for the preparation of men for public service, like law and government.