What do Jehovah's Witnesses preach?

Answer 1

That God will soon intervene in human affairs and put an end to suffering establishing a paradise earth (Revelation 21:4, 5).

According to Wikipedia [quote]

"The stated purpose of The Watchtower [their principle bible instructional journal], as suggested by its subtitle, Announcing Jehovah's Kingdom, is to draw attention to the kingdom of God, which Jehovah's Witnesses believe is a real government that will soon replace all earthly governments. The inside cover page of each issue has the following mission statement:

'THE PURPOSE OF THIS MAGAZINE, The Watchtower, is to honor Jehovah God, the Supreme Ruler of the universe. Just as watchtowers in ancient times enabled a person to observe developments from afar, so this magazine shows us the significance of world events in the light of Bible prophecies. It comforts people with the good news that God's Kingdom, which is a real government in heaven, will soon bring an end to all wickedness and transform the earth into a paradise. It promotes faith in Jesus, who died so that we might gain everlasting life and who is now ruling as King of God's Kingdom.[...]'"