In Christianity, Jesus is the mediator for all mankind. The Bible states at 1 Timothy 2: 5, 6:
“For there is one God, and one mediator between God and men, a man, Christ Jesus, who gave himself a corresponding ransom for all”
However, the Watchtower Society doctrine on the matter differs from what the scriptures state. It is summed up in their publication Worldwide Security Under the "Prince of Peace" on page 10, paragraph 16:
“Likewise, the Greater Moses, Jesus Christ, is not the Mediator between Jehovah God and all mankind. He is the Mediator between his heavenly Father, Jehovah God, and the nation of spiritual Israel, which is limited to only 144,000 members.”
Further explanation of their stance by the Watchtower Society can be seen in such articles as the Watchtower November 15, 1979, page 27, 'One Mediator Between God and Men':
"They recognize that they are not spiritual Israelites in the new covenant mediated by Jesus Christ, nor part of the “chosen race, a royal priesthood, a holy nation.”...Yet they do benefit from the operation of the new covenant. They benefit from this just as, in ancient Israel, the “alien resident” benefited from residing in among the Israelites who were in the Law covenant...To keep in relationship with “our Savior, God,” the “great crowd” needs to remain united with the remnant of spiritual Israelites."
Most congregations of Jehovah's Witnesses do not have these "spiritual Isrealities" [Also called "The Anointed" by the Watchtower Society] within their midst. Even congregations which do have "The Anointed", they are not the ones who provide directions to Jehovah's Witnesses. It is the Governing Body; a select few older men located in Brooklyn, NY who serve as the leaders and provides the doctrine and teachings for Jehovah's Witnesses which they must follow. Under the terminology "Faithful and Discreet Slave Class" these older men are the ones who in effect serve as a mediator for Jehovah's Witnesses. They are taught to believe that direction and instruction coming from the "Faithful and Discreet Slave Class" is coming from God.
The most significant reason the Watchtower Society teaches Jesus mediating only for the Anointed is that the Bible shows the New Covenant setup by Jesus Christ provides a heavenly resurrection, and the doctrine of the Watchtower Society is only 144,000 will have a resurrection to heaven. Therefore, Jesus as a mediator is only applicable to them.
This whole notion still taught today by the Watchtower Society was started by the Watchtower Society's second president, 'Judge' Rutherford. The Watchtower April 1, 1934 on page 104 states the following:
"Christ Jesus is the mediator of the new covenant toward his own brethren, that is to say, spiritual Israel, during the period of time God is taking out from the nations a people for his name."
It was the idea and belief of one man - Rutherford - which is still taught as truth by Jehovah's Witnesses today. Rutherford naturally aligned himself as being one of the anointed. This assists in the belief of salvation being dependent on belonging to the organization. The organization is supposedly led by anointed men and/or they "appoint" those who take the lead, those not of the anointed or not appointed need to follow those who fall into such categories.
Nevertheless, once again the scriptures are clear on the matter of mediator...
1 Timothy 2:5, 6:
“For there is one God, and one mediator between God and men, a man, Christ Jesus, who gave himself a corresponding ransom for all”
The Jehovah’s Witnesses annual report for 2008 shows 9,986 as being of the anointed. Those are the only ones who have Jesus as their Mediator according to Watchtower Society's teaching. All other Jehovah's Witnesses are without a mediator, and are given an organization to follow.