The Watchtower says they must be obeyed because they are 'God's slave'  and channel of communication . However, on rare occasions, perhaps as a disclaimer, they have admitted having no divine inspiration. Take a look at what they say in their literature.
"This pouring out of God's spirit upon the flesh of all his faithful anointed witnesses [Joel 2:28-29] does not mean those now serving as Jehovah's Witnesses are inspired. It does not mean that the writings in this magazine The Watchtower are inspired and infallible and without mistakes. It does not mean that the president of the Watch Tower Bible and Tract Society is inspired and infallible, ..." (Watchtower May 15, 1947, 157)
"... Because it [Watch Tower Society] is not infallible and has never claimed to be, from time to time corrections are necessary." (Watchtower Oct 15, 1954, 638)
'the New World Translation has endeavored to put God’s Word as contained in the original Greek into these languages with the “correct words of truth” in each language. No claim of divine inspiration is made for these translations in modern-day language.' Watchtower Nov 15, 1969, Article: “Between-the-Lines” Translations of the Bible, par. 23.
"True, the brothers preparing these publications are not infallible. Their writings are not inspired as are those of Paul and the other Bible writers." (Watchtower, Feb. 15, 1981, page 19)
"The Governing Body consists of a group of anointed Christian men ... They are not inspired of God and hence are not infallible." (Jehovah's Witnesses Unitedly Doing God's Will Worldwide brochure , 26) 
How can the Watchtower be God's channel of communication and 'God's organization' if they have no 'angelic revelations or divine inspiration'?
If they can mistakes like any other religion, how can they say all other spiritual teachers are 'false', mentally diseased, or possessed by demons?
Do we deserve the truth? What does the Watchtower say?
'No harm is practiced, however, by withholding incriminating information from one who is not entitled to know. ... Various characters of the Bible have been accused of lying, such as Jacob, Rahab, the Gibeonites, David and others, but there is no record in the Bible that they came under divine disapproval for this.' Watchtower Oct 1, 1954, 'Christians Live the Truth', par 21, 25. Are you entitled to know the truth? Is it true that the Bible gives us a license to withhold the truth? Are they acting in harmony with what the Bible says? Read more about why it's ok to withhold truthful information
Theocratic Warfare is a code word for withholding the truth from non believers and 'enemies'. However, critics say that the organization withholds truthful information from Jehovah's Witnesses as well. Elders have access to secret information that women and ordinary Jehovah's Witnesses don't have. Why do they hide the truth? See Jehovah's Witness Rules - Secret Information For Elders Only
'By word or action, may we never challenge the channel of communication that Jehovah is using today. ... we should cherish our privilege to cooperate with the slave class.' Watchtower Nov 15, 2009, article, 'Treasure Your Place in the Congregation', par 5. In the same article, the organization cautions Jehovah's Witnesses against disobedience, disrespect, and a spirit of independence. JW's are told to be obedient and submissive to those taking the lead. See God's channel of communication
What is the truth? The Watchtower has no divine inspiration. Everything they teach could be false. The reason why they boast about being 'God's organization', 'channel of communication', 'faithful and discreet slave', ... etc. is obvious. They want to be obeyed. They don't want any to dare question anything they teach.
The Watchtower tricks people into believing everything they teach comes directly from the Bible and thus comes from God Himself. Although they quote scriptures to support everything they say, a close examination of those scriptures doesn't prove the Watchtower and it's Governing Body has the authority of God. See Mind Control
Watchtower quotes about being God's 'faithful and discreet slave'
Watchtower quotes about being God's channel of communication
Watchtower quotes: Obey Us