Christians know that it is now HEAVENLY JERUSALEM that is the focus of God's plans. You have apparently missed Jesus' declaration concerning earthly Jerusalem: "I say to you, The kingdom of God will be taken from you and given to a nation producing its fruits." (Matt.21:43)
"But YOU [Christians] are 'a chosen race, a royal priesthood, a holy nation, a people for a special possession,' that you should declare abroad the excellencies of the one that called you out of darkness into his wonderful light. For you were once not a people, but are now God's people." (I Peter 2:9,10)
"We have such a high priest as this, and he [Jesus] has sat down at the right hand of the throne of the Majesty in the heavens, a public servant of the holy place and of the true Temple, which God put up, and not man." (Hebrews 8:1,2)
Jesus' Kingdom will always be in heaven. He can guide us just fine from there. As Galatians 4:26 says: "The Jerusalem above is free, and she is our 'mother.'" In chapter 6 it is stated that JESUS' death is the center of what Christians should be looking at, and "the Israel of God" is "all those who walk orderly by this rule of conduct," that is, boasting only in Christ.
Do you see that? "The Israel of God" is now the Christian congregation.
Yes but what YOU do not see is
a)
Jerusalem is to descend from heaven and be planted on earth
B)
God's plan for the fullness of time [a synonym for the 1,000 years) is to UNITE ALL THINGS in Christ whether they be things in heaven or things on earth.
Now we see not that all things at the present time are united to Christ and He tells us that right up to the time of His coming they will not be united...therefore there is an age yet to come