This line is cited in Debrunner, 1979. It describes the testimony of a Portuguese man, D’ Azurara, when he saw African slaves arriving in Lagos, Portugal during the reign of Henry the Navigator (1394-1460).
While the speaker pities the fate of the slaves, he claims that a better fate is waiting for them, as they will be taken in to Portuguese houses, taught the doctrine of Christianity and get acquainted with Portuguese culture.
Portraying African cultures and religions as savage or primitive was a common rhetorical device to defend slavery, by portraying Europeans as saviors.
