What was mcduffies religious argument for slavery

I believe this is your answer. George McDuffie is a South Carolina governor on 1834 to 1836. On his 1835 speech regarding slavery and explained why slavery must not be ruled out in two points: (1) his racial argument is that African-Americans are born to be slaves because of their physical attributes which was evidently shown with their skins. He said that it is useless to gain power if you have an inferior skin; and (2) his religious argument is that God decided to make African-American slaves when he created them and that there is nothing they can do about it.

the crusaders are identified in the painting;

c. by the red crosses on their backs