A book that every Christian ought to read it would be key to their knowledge of God, and Grace of God provided through the editorial work of His Son the God/man redeemer Jesus the Christ, and sovereignly and graciously applied by the Holy Spirit.
Obtain a clear understanding of the Cosmic Rebellion in the fall and the resulting Radical Depravity of humanity.
Reading this book will give a joyous reflection on the gods Free Grace, the regeneration of sinners Adoption and the mystical union with Christ.
Then looking forward to ones Eternal State of Either Eternal Blessedness or eternal misery ( )

Read ToC to see best spots in section 3, which is the best section of the book. Beautiful section on conversion. ( )