There were commands against mixing together things that are supposed to be apart. Many scholars believe the underlying point was spiritual - it was about purity and holiness, and not mixing the clean and unclean.
What was the significance of the commands against mixing different things in Deuteronomy 22:9–11? Do any of the laws regarding mixing given in Deuteronomy 22 apply today?
www.gotquestions.org
Atheists who keep a collection of "oh but what about" verses from the depths of the Old Testament tend, in my experience, to not really be interested in learning the answers.