When the last of these approved spiritual Israelites cease to be ‘men’ because of earthly death and a resurrection to a share in the heavenly kingdom, then the mediatorship of Jesus Christ will cease also.
The WT hates Jesus. The little peasant boy from nowhereville who defeated Satan and saved anyone who wanted it. And, they especially hate how simple God made it for "whosoever" to inherit everlasting life and membership into the family of God. Satan is a defeated enemy, and these kinds of scams are all he is able to do while he awaits his final home - Eternity in the Lake of Fire.