Slaves were allowed to practice Christianity because :

Slave Christianity. In the United States, Christianity not only held views about slavery but also on how slaves practiced their own form of Christianity.

Slaves were allowed to practice Christianity because people in the United States were concerned about how Christianity was practiced by slaves.

Explanation:

Some people in the United States believed that the different elements of African culture had been destroyed because of the horrific experiences that Africans experienced when they were obliged to come to the United States.

However, after the work done by Melville Herskovits in 1941, scholarship found an interesting relationship between African and Christian religious tradition, because according to scholarship slaves took to the United States an important variety of aspects in terms of religious traditions. They include tribal shamanism as well as Islam.