The Watch Tower Bible and Tract Society of Pennsylvania is a nonprofit corporation formed in 1884 under the laws of the Commonwealth of Pennsylvania, U.S.A. It is used by Jehovah’s Witnesses to support their worldwide work, which includes publishing Bibles and Bible-based literature.
According to its charter, the corporation’s purposes are “religious, educational, and charitable,” in particular, to “preach and teach the gospel of God’s Kingdom under Christ Jesus.” Membership in the corporation is by invitation only and is not based on how much a person has donated. The corporation members and directors assist the Governing Body of Jehovah’s Witnesses.
The Knowledge book was the main publication of the Society for use in conducting home Bible studies. It allowed teachers to teach Bible truth with simplicity, clarity, and brevity. It replaced the publication "You Can Live Forever in Paradise on Earth."
It is no longer in print. It was replaced by the publication, "What Does the Bible Really Teach?", which is available online at the JW.org website, or one of Jehovah's Witnesses can drop one off at your house, free of charge.