Only 144,000 In The New Covenant?

You may or not be aware that the Watchtower teaches that Jesus is not the Mediator between God and men. They teach that Jesus Mediates between God and their remnant of the 144,000 anointed Christians. They have gone to great lengths to spread this doctrine and make sure that millions understand that they have no hope for eternity in heaven. But is this Biblical?

How can they teach this when Galatians 4:22-31 makes a strong case for Millions of people being in the New Covenant? Let's read what their own New World translation says.

Galatians 4:22-31
22 For example, it is written that Abraham acquired two sons, one by the servant girl and one by the free woman; 23 but the one by the servant girl was actually born in the manner of flesh, the other by the free woman through a promise. 24 These things stand as a symbolic drama; for these [women] mean two covenants, the one from Mount Si′nai, which brings forth children for slavery, and which is Ha′gar. 25 Now this Ha′gar means Si′nai, a mountain in Arabia, and she corresponds with the Jerusalem today, for she is in slavery with her children. 26 But the Jerusalem above is free, and she is our mother.
27 For it is written: “Be glad, you barren woman who does not give birth; break out and cry aloud, you woman who does not have childbirth pains; for the children of the desolate woman are more numerous than [those] of her who has the husband.” 28 Now we, brothers, are children belonging to the promise the same as Isaac was. 29 But just as then the one born in the manner of flesh began persecuting the one born in the manner of spirit, so also now. 30 Nevertheless, what does the Scripture say? “Drive out the servant girl and her son, for by no means shall the son of the servant girl be an heir with the son of the free woman.” 31 Wherefore, brothers, we are children, not of a servant girl, but of the free woman.