Step-by-step explanation:
The religion in the middle age was the most important aspect in the lives and social functioning of many countries across Europe.
The Catholic church had an enormous influence was the most important religious entity of the era, so besides the personal conviction of many explorers (Prince Henry included), to extend the ¨Word of god¨ to pagan lands, it was a huge help for them to have the Catholicism backup, for the newly conquered lands, and their own kingdoms (Portugal kingdom, in this case).