The kingdom of heaven is Spiritual Israel serving with Jesus. 144,000 + 1.
Ex 19:5,6 "Now if you will strictly obey my voice and keep my covenant, you will certainly become my special property* out of all peoples, for the whole earth belongs to me. You will become to me a kingdom of priests and a holy nation."
That was for Israel.
Then 2 Sam 7 Nathan tells David that his offspring will sit on Jehovah's throne forever. That was a propesy leading to Jesus. But Jesus lived and died and never became king. What gives? Did the prophesy fail?
Israel was unfaithful. Dan 4 tells of a tree, a kingdom that was banded for 2520 years.
Jesus had to wait until it was unbanded to become king.
In the meantime - Jeremiah tells us that Israel was replaced, old covenant with a new one.
Physical Israel for Spiritual. Grafting of the olive tree. Lopping off the unfaithful Israelites and replacing them with gentiles. This indicates that Paul had some idea that the structure of the spiritual temple was limited. But it seems that he and Jesus did not know that only 144,000 would be anointed with holy spirit and be kings and priests with Jesu.
Peter said 1 Pet 2:8 "But you are “a chosen race, a royal priesthood, a holy nation, a people for special possession, that you should declare abroad the excellencies” of the One who called you out of darkness into his wonderful light." He quotes from Ex 19 saying that his readers are the fulfillment of the promised to Israel.
When the bands of the tree were opened as the 7 times ended. Well, we don't exactly know when it started by it was around 607-605 and ended 1914-1916. Then the kingdom was established, Jesus became king in the heavens. It had to be invisible as Jesus is a spirit and the heavens are spirits. Jesus cleaned the heavens. Which shows that he is Michael as he said in John 14:2 "In
the house of my Father are many dwelling places. Otherwise, I would
have told you, for I am going my way to prepare a place for you. Also,
if I go my way and prepare a place for you, I will come again and will
receive you home to myself, so that where I am you also may be."
He prepares a place for them by cleansing the heavens and kicking Satan and his demons out.
That clearly shows that Michael doing what he did in Rev 12:7-9 is Jesus (unless Jesus delegated it to a separate angel named Michael), except that Jesus said "I am going my way to prepare a place for you". He does the preparing.
But anyway, that is the kingdom.
Jesus and 144,000 spiritual Israelites serving in heaven as kings and priests over the earth.