Which 1615 Galileo letter defended Copernicanism while discussing biblical interpretation?

The 1615 letter in which Galileo defended Copernicanism while discussing biblical interpretation was the Letter to the Grand Duchess Christina.

Galileo wrote it for Christina of Lorraine, Grand Duchess of Tuscany, amid growing controversy over whether Earth’s motion contradicted Scripture. The work argued that God created both nature and the Bible, so genuine physical evidence and Scripture cannot ultimately conflict. When apparent conflict arises, Galileo said, interpreters should reconsider overly literal readings of passages written in ordinary language.

The letter drew especially on Augustine and addressed passages such as the biblical account of Joshua commanding the Sun to stand still. Galileo argued that Scripture teaches matters of salvation rather than functioning as a technical astronomy textbook. The text was therefore both a defense of Copernican astronomy and an influential statement about science, theology, and interpretation.

A common mix-up is to choose Galileo’s other works. The Assayer concerns physical reasoning and comets, while Discourse on Floating Bodies examines buoyancy and motion. Neither is the 1615 biblical and Copernican treatise.