It's unfortunate that the term Millennial Kingdom is in use. Without the proper exegesis it leads to the kind of misunderstanding that we are seeing here.
The term Kingdom of Heaven appears 33 times in the New Testament -- in every single case it is referring to the kingdom of the heavenly realm where Jesus sits with God right now, and that will ultimately be the seat of the New Heaven and the New Earth, in the New Jerusalem.
The term Kingdom of God appears 69 times in the New Testament -- in every single case it is referring to the kingdom of the heavenly realm where Jesus sits with God right now, and that will ultimately be the seat of the New Heaven and the New Earth, in the New Jerusalem.
There are a smattering of other references to the heavenly Kingdom, many having the "of heaven" or "of God" implied.
And there are many mentions of other kingdoms, virtually all in terms of physical, earthly kingdoms. In at least one case, Matthew 12:26, Satan is even credited with having a kingdom.
Then there are 47 mentions in Old and New Testament to David's Kingdom -- in virtually every single case referring to a physical earthly throne sat on, first, by David himself, and then, later, by Jesus during his physical reign on earth (during the Millennium).
That's why it's important to understand the difference between references to the two Kingdoms that Christ will reign over. Currently, He reigns with his Father in the heavenly Kingdom. When He returns to end the Great Tribulation He will reign for 1,000 years on a physical, earthly Throne of David (as promised in many places in Scripture). Then at the end of the 1,000 years the physical earthly throne will be no longer, and He will reign once again with his Father on the throne in the New Jerusalem in the New Heaven and the New Earth.
Long story short, you can't say Millennial Kingdom and apply that to the heavenly Kingdom of God. It's not the same thing.
Here's Jesus on the kingdom;
Please consider the spiritual nature of the Kingdom:
“And saying, Repent ye: for the kingdom of heaven is at hand.” (Matthew 3:2) (KJV 1900)
“And from the days of John the Baptist until now the kingdom of heaven suffereth violence, and the violent take it by force.” (Matthew 11:12) (KJV 1900)
“Verily I say unto you, There be some standing here, which shall not taste of death, till they see the Son of man coming in his kingdom.” (Matthew 16:28) (KJV 1900)
“Now this I say, brethren, that flesh and blood cannot inherit the kingdom of God; neither doth corruption inherit incorruption.” (1 Corinthians 15:50)
“Jesus answered and said unto him, Verily, verily, I say unto thee, Except a man be born again, he cannot see the kingdom of God.” (John 3:3) (KJV 1900)
“Jesus answered, “I tell you the solemn truth, unless a person is born of water and spirit, he cannot enter the kingdom of God.” (John 3:5)
“Jesus answered, My kingdom is not of this world: if my kingdom were of this world, then would my servants fight, that I should not be delivered to the Jews: but now is my kingdom not from hence.” (John 18:36) (KJV 1900)
“And when he was demanded of the Pharisees, when the kingdom of God should come, he answered them and said, The kingdom of God cometh not with observation:” (Luke 17:20) (KJV 1900)
“Neither shall they say, Lo here! or, lo there! for, behold, the kingdom of God is within you.” (Luke 17:21) (KJV 1900)
“But if I cast out demons by the finger of God, then the kingdom of God has already overtaken you.” (Luke 11:20)
“because we are not looking at what can be seen but at what cannot be seen. For what can be seen is temporary, but what cannot be seen is eternal.” (2 Corinthians 4:18)
“Now when the people saw the miraculous sign that Jesus performed, they began to say to one another, “This is certainly the Prophet who is to come into the world.” Then Jesus, because he knew they were going to come and seize him by force to make him king, withdrew again up the mountainside alone.” (John 6:14–15)
“He delivered us from the power of darkness and transferred us to the kingdom of the Son he loves,” (Colossians 1:13)
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When Jesus saw that he answered intelligently, He said to him, “You are not far from the kingdom of God.” And no one dared to question Him any longer.” (Mark 12:34) (HCSB)
“for the kingdom of God is not eating and drinking, but righteousness, peace, and joy in the Holy Spirit.” (Romans 14:17) (HCSB)