Dark and terrible as is this picture, I hold it to be strictly true of the overwhelming mass of professed Christians in America. They strain at a gnat, and swallow a camel. (Appendix.4)
One of the ways Douglass shows himself to be a true Christian (while slaveholders are not) is by quoting the Bible. The part about the gnat and camel comes from Matthew 23:24, where Jesus is rebuking the Pharisees for their hypocrisy.