1. Based on my previous tweet about natural law theory, I was asked to provide some recommended resources. Here are just a few that I would strongly recommend as well as a brief explanation for why.
2. Natural Law: A Brief Introduction and Biblical Defense by David Haines and Andrew Fulford.
This is short, accessible, and deeply informed by exegesis and rigorous philosophy. If you're looking for an affordable introduction, this is probably it. https://www.amazon.com/Natural-Law-Introduction-Biblical-Davenant/dp/0999552724/ref=sr_1_1?dchild=1&keywords=Andrew+fulford+natural+law&qid=1606941448&sr=8-1
This is short, accessible, and deeply informed by exegesis and rigorous philosophy. If you're looking for an affordable introduction, this is probably it. https://www.amazon.com/Natural-Law-Introduction-Biblical-Davenant/dp/0999552724/ref=sr_1_1?dchild=1&keywords=Andrew+fulford+natural+law&qid=1606941448&sr=8-1
3. Abolition of Man by C. S. Lewis.
What can I say? Its Lewis. This is a primer I wish every Christian would read. Lewis brilliantly demonstrates that discarding the natural law means discarding such realities as beauty and basic normative claims. https://www.amazon.com/Abolition-Man-Education-Develops-Morality/dp/B00U93AFPI/ref=sr_1_8?dchild=1&keywords=the+abolition+of+man&qid=1606941705&sr=8-8
What can I say? Its Lewis. This is a primer I wish every Christian would read. Lewis brilliantly demonstrates that discarding the natural law means discarding such realities as beauty and basic normative claims. https://www.amazon.com/Abolition-Man-Education-Develops-Morality/dp/B00U93AFPI/ref=sr_1_8?dchild=1&keywords=the+abolition+of+man&qid=1606941705&sr=8-8
4. What We Can't Not Know by J. Budziszewski.
This is a very fun read and simply demonstrates how so many truths we operate our lives by are indemonstrable, underivable, and obvious. We deny natural law only at the expense of denying reality. https://www.amazon.com/What-We-Cant-Not-Know/dp/1586174819/ref=sr_1_4?crid=2W6JQPPQC3UPS&dchild=1&keywords=j.+budziszewski&qid=1606941751&sprefix=j.+bu%2Caps%2C187&sr=8-4
This is a very fun read and simply demonstrates how so many truths we operate our lives by are indemonstrable, underivable, and obvious. We deny natural law only at the expense of denying reality. https://www.amazon.com/What-We-Cant-Not-Know/dp/1586174819/ref=sr_1_4?crid=2W6JQPPQC3UPS&dchild=1&keywords=j.+budziszewski&qid=1606941751&sprefix=j.+bu%2Caps%2C187&sr=8-4
5. Retrieving the Natural Law by J. Daryl Charles.
More academic, this lays out the case for why Protestants need more natural law theory, not less. https://www.amazon.com/Retrieving-Natural-Law-Critical-Bioethics-ebook/dp/B001GIOC4K/ref=sr_1_13?crid=TJ710KCQFBI2&dchild=1&keywords=j.+daryl+charles&qid=1606941862&sprefix=j.+daryl+ch%2Caps%2C190&sr=8-13
More academic, this lays out the case for why Protestants need more natural law theory, not less. https://www.amazon.com/Retrieving-Natural-Law-Critical-Bioethics-ebook/dp/B001GIOC4K/ref=sr_1_13?crid=TJ710KCQFBI2&dchild=1&keywords=j.+daryl+charles&qid=1606941862&sprefix=j.+daryl+ch%2Caps%2C190&sr=8-13
6. The Cambridge Companion to Natural Law Ethics
Technical volume, but wide-ranging on the overall field of natural law theory. https://www.amazon.com/Cambridge-Companion-Natural-Companions-Philosophy/dp/1108435610/ref=sr_1_1?dchild=1&keywords=Cambridge+companion+to+natural+law+ethics&qid=1606941971&sr=8-1
Technical volume, but wide-ranging on the overall field of natural law theory. https://www.amazon.com/Cambridge-Companion-Natural-Companions-Philosophy/dp/1108435610/ref=sr_1_1?dchild=1&keywords=Cambridge+companion+to+natural+law+ethics&qid=1606941971&sr=8-1
7. Clash Of Orthodoxies: Law Religion & Morality In Crisis by @McCormickProf. He has more technical works, but this is a good beginning place for the application of natural law to contemporary issues. https://www.amazon.com/Clash-Orthodoxies-Religion-Morality-Crisis/dp/1882926943/ref=sr_1_2?crid=3VKWEIEXQMPVJ&dchild=1&keywords=the+clash+of+orthodoxies&qid=1606942271&sprefix=the+clash+of+ortho%2Caps%2C179&sr=8-2
8. What is Marriage?: Man and Woman: A Defense by @RyanTAnd, @McCormickProf, and Sherif Girgis. This is natural law theory applied to the marriage question. https://www.amazon.com/What-Marriage-Man-Woman-Defense/dp/1594036225/ref=sr_1_2?crid=27PHFSF9OEN9D&dchild=1&keywords=what+is+marriage+man+and+woman+a+defense&qid=1606942367&sprefix=what+is+marriage%2Caps%2C182&sr=8-2
9. I would be remiss not to mention my forthcoming book, Liberty for All, which attempts to connect religious liberty to Christian theology and natural law reasoning: https://www.amazon.com/Liberty-All-Defending-Everyones-Pluralistic/dp/1587434490/ref=sr_1_4?crid=NG4HSH0JQIDY&dchild=1&keywords=liberty+for+all+walker&qid=1606942573&sprefix=liberty+for+all%2Caps%2C185&sr=8-4
10. Biblical Natural Law: A Theocentric and Teleological Approach by Matthew Levering. This is a tremendous one volume explanation of natural law from start to finish. https://www.amazon.com/Biblical-Natural-Law-Theocentric-Teleological/dp/0199654115/ref=sr_1_2?dchild=1&keywords=biblical+natural+law&qid=1606944285&sr=8-2
11. Divine Covenants and Moral Order: A Biblical Theology of Natural Law.
This is a long, but masterful demonstration of natural law as sequentially worked out through the unfolding of the covenantal drama in Scripture. https://www.amazon.com/Divine-Covenants-Moral-Order-University/dp/0802870945/ref=sr_1_2?crid=UY8XE3WCHGP6&dchild=1&keywords=divine+covenants+and+moral+order&qid=1606944390&sprefix=divine+covenant%2Caps%2C184&sr=8-2
This is a long, but masterful demonstration of natural law as sequentially worked out through the unfolding of the covenantal drama in Scripture. https://www.amazon.com/Divine-Covenants-Moral-Order-University/dp/0802870945/ref=sr_1_2?crid=UY8XE3WCHGP6&dchild=1&keywords=divine+covenants+and+moral+order&qid=1606944390&sprefix=divine+covenant%2Caps%2C184&sr=8-2
12. There are many, many more books I could recommend, so please accept these recommendations as only the tip of the iceberg to a very rich, long tradition of Christian moral thought.