What is this book about?

This book is a comprehensive guide to the Christian's spiritual life, emphasizing the assurance of salvation and the preservation of spiritual health. Gill systematically explores the 'experiments' or experiences that mark the spiritual journey of a believer. He delves into the nature of assurance, explaining it not as a feeling but as a confident certainty based on God's promises and the work of Christ. The book then outlines the 'preservatives' or practices necessary to sustain this spiritual life, countering common 'evils' or hindrances that can undermine faith and assurance.