The Holy Spirit
The fraud and manipulation, which abounds in the church under the pretence that it is the work of the Holy Spirit, make this book required reading. Things excellent in themselves and acknowledged by all Christians are often counterfeited; the more worthy any thing is, the more destructive is the abuse of it.
All believers must "try the spirits" because false prophets and false teachers deprive us of liberty. Some people claim to know the Spirit's inward enlightenment, but the darkness of Satan fills their imaginations. This false light is of no use to the souls of men; it is in opposition to Christ and his work. The only way to tackle this is by giving a plain and scriptural account of the nature and work of the Holy Spirit. His work did not end at Pentecost, otherwise all faith in Christ would have ceased, and Christianity also. The Spirit continues to work in the hearts of men, convicting of sin; producing godly sorrow and humility; regenerating and sanctifying; supplying grace and helping in prayer.
John Newton spoke of Owen's work as, "An epitome, if not the masterpiece of his writings." No one who cares about the church in the 21st century can afford to ignore this exhaustive guide.
"I assert unhesitatingly that the man who wants to study experimental theology will find no books equal to those of Owen for complete scriptural and exhaustive treatment of the subjects they handle. If you wish to study thoroughly the doctrine of sanctification I make no apology for strongly recommending Owen on the Holy Spirit."
—J. C. Ryle