How does sewall appeal to christians in this excerpt?

1- Mr Sewall was refereing to a biblical scenario, The one of Joseph, to talk about how slavery should not be considered whatsoever. 
2- He refered to three major arguments to defend his abolitional document: African slaves were descended from Adam and Eve, Israelites were expressly forbidden from buying and selling slaves and The enslave,net of Joseph was illegal and immoral.
3- Based on this document, Sewall appealed to christians by leading them to the immediate emancipation of countless slaves.

The one that starts with the guest is concerned.