Question

What does equiano mean when he refers to "nominal christians"?

Answer 1

You don't give us a clue as to who Equiano is or where he or she used this phrase, but "nominal" in this phrase apparently means "in name only." It apparently means "people who call themselves Christians but (by some definition or other) are not really Christians."

Answer 2

Equino calls the white people nominal Christians because their actions do not match their words