There are good reasons why it's hard to convert a Jehovah's Witness to Christianity. They will not to listen to anything you say, unless you bring up logical questions they haven't thought of before. Even then you will need to give them time to research and consider the implications of leaving the Watchtower Society.
Almost all Witnesses secretly have nagging doubts about their faith but no one is allowed to challenge doctrines. Disfellowshipped Witnesses are completely cut off from all contact with their friends and family members who don't live in the same house. For this reason alone, they will defend all teachings of the Watchtower at all costs even if they don't believe everything they're told.
Critics say faulty assumptions, mind control, propaganda, hypnotic suggestions, and brainwashing is used to make Jehovah's Witnesses fear and distrust everyone who disagrees.
The anonymous writers of Watchtower publications are so good at mind control techniques, that no one notices what they're doing.
The fact of the matter is that Jehovah's Witnesses will instantly shut down and immediately reject any opposing idea as 'persecution' and the deceitful tactics of Satan to turn them away from the God. Why? Because they believe their organization is run by God and their doctrines are Bible based. Therefore all opposing viewpoints don't come from God.
Satan the Devil is a very real spirit angel as far as Jehovah's Witnesses are concerned. He is a big part of the fear programming Jehovah's Witnesses receive on a daily basis from their literature, Kingdom Hall meetings, conventions, assemblies, and day to day conversations with fellow believers. See Temptations of The Devil
Jehovah's Witnesses are taught that their faulty New World Translation of the Bible is the best, and they believe they are the only ones with the true religion. All other viewpoints and interpretations are considered valueless, worthless, and 'false'. They believe that anyone who speaks out against the organization is committing a sin against God.
Jehovah's Witnesses receive the same messages over and over again. Their entire life revolves around studying Watchtower publications, preparing for meetings, attending five meetings a week, and finding new members for the organization. Much of their free time is spent discussing Watchtower doctrines with fellow Witnesses. Since independent thinking can result in disfellowshipping from the organization, very few Witnesses are willing to challenge the Watchtower's authority. No one wants to lose their family and close friends. And no one wants to be hated as an apostate.
People who have left the organization and are trying to help their friends break free from the fictional world of the Watchtower, are considered 'the enemy'. However the real enemy lurks in the darkness. Consider the Watchtower doctrine of theocratic warfare. Some say there is evidence that theocratic war is actively being used to hide the truth and keep Jehovah's Witnesses loyal to their religion at all costs.
Even though professionals say that the mental illness is higher among the Jehovah's Witnesses than in other religion, most Jehovah's Witnesses appear to be very happy - at least on the surface. Most are convinced that the Watchtower has their best interests at heart and they don't want to leave.
They are happy because they feel safe, secure, and loved. However it's a false sense of security. Jehovah's Witness are programmed to believe the world is 'their enemy' and the Watchtower is their friend.
Furthermore they are convinced that the only way to be saved and attain 'everlasting life' is to be obedient to all the teachings of the 'faithful and discreet slave'. This doctrine causes Jehovah's Witnesses to stop listening the moment they hear anything negative about their religion.
Jehovah's Witnesses strongly believe they must remain loyal to the the organization and the 'slave' to attain everlasting life. For Jehovah's Witnesses the idea of obeying the words of Jesus alone is not good enough. However the Bible disagrees.
John 6:67-69 says, "You do not want to leave too, do you?" Jesus asked the Twelve. Simon Peter answered him, "Lord, to whom shall we go? You have the words of eternal life. We believe and know that you are the Holy One of God."
Peter said Jesus has the words of eternal life. Nothing was mentioned about any religion or the Watchtower. True christians do not follow the apostles, the early christian congregation, the 'entire' Bible, or any modern day organization. Peter said that only Jesus has 'the words of eternal life'.
The wordology Jehovah's Witnesseses keeps them menally trapped by deep rooted beliefs. They feel compelled to obey the organization and discredit anything you might say. A perfect example of this is are these words 'Jehovah, the truth, the true religion, false religion, Jehovah's organization, Jehovah's modern day representatives, Jehovah's visible organization, like minded, the faithful and discreet slave, end of this system of things, separate from the world, God's people, rebellion against Jehovah, and being 'in the truth'. Jehovah's Witnesses are not aware how many times they say or think about theses words because they say them so often.
Anyone who receives controlling messages repeatedly from family, friends, and Watchtower publications, falls into a trance-like state. They may find themselves doing and saying things automatically without any thought.
Mental programming and the severe consequences of leaving, makes it hard to convert a Jehovah's Witness to Christianity (or any other religion), even when they don't agree with some or even all doctrines.
Fortunately there are some big issues you can make them aware of. By patiently asking them logical questions about things they do not know, you can plant the seeds of doubt. This is the first step in converting a Jehovah's Witness to Christianity.