I just completed this work by Spurgeon (the audio book version) and found it to be a wealth of encouragement for those who wrestle with their assurance of salvation. It was also a deep source of doctrinal truths regarding God’s grace and provision for salvation; helping me to better understand that salvation is all of God. I recommend it to those who are looking for a great exposition on the truths of the doctrines of grace.

This whole book is available to read online here.