“On the Bondage of the Will”
From Wikipedia:
“On the Bondage of the Will”, by Martin Luther, argued that people can only achieve salvation or redemption through God, and could not choose between good and evil through their own willpower. It was published in December 1525. It was his reply to Desiderius Erasmus’ De libero arbitrio diatribe sive collatio or On Free Will, which had appeared in September 1524 as Erasmus’ first public attack on Luther. The debate between Luther and Erasmus is one of the earliest of the Reformation over the issue of free will and predestination.”
It is slow read, but it is an important book in the history of Truth.
A free PDF download can be retrieved from the Internet Archive using this link.
This translation has the Forward by J.I. Packer, which in itself is a most important item to read.