3. Kingdom of Heaven
The book of Matthew commonly uses the phrase “The Kingdom of Heaven”, while in the rest of the New Testament the similar phase of “The Kingdom of God” is used instead. That raises the question of whether these mean the same thing, or whether they are describing two different kingdoms, or different aspects of that kingdom.
The Greek word translated “God” in the New Testament is “Theos”, and has a broad meaning of diety. “Heaven” is quite a different term and literally just means the sky or a high place. It is associated with the dwelling place of God though, and so bears a close relationship. At times the Jews used the term “heaven” as an idiom for “God” or even in the style of a euphemism. This was to avoid addressing God in a non-reverential way, similar to how modern translations of the Bible still use the term “the Lord” in the place of the name of God.
There is an example of this in the parable of the prodigal son, where the son returns and recognises his sin. The sin is against God, but the returning son uses the term “heaven” to refer to this.
Luke 15:17: But when he came to himself he said, `How many hired servants of my father's have bread enough to spare, and I'm dying with hunger! 18. I will get up and go to my father, and will tell him, "Father, I have sinned against heaven, and in your sight. WEB
Contrasting to this, David in the Psalms uses the same language, but is explicit in referring to God,
Psalm 51:1: Have mercy on me, God, ... 4. Against you, and you only, have I sinned, ... WEB
It would appear that Matthew was writing with this Jewish influence or to a Jewish audience and so used this term. This does not mean that “heaven” is the same in meaning to “God” in the writing of Matthew, as “heaven” is also used in much more specific and literal circumstances.
One of several examples of how “Kingdom of God” and “Kingdom of Heaven” occurs with the parallel record of the analogy with the mustard seed. This are recorded in both Matthew and Mark.
Matthew 13:31: He set another parable before them, saying, "The Kingdom of Heaven is like a grain of mustard seed, which a man took, and sowed in his field; WEB
Mark 4:30: He said, "How will we liken the Kingdom of God? Or with what parable will we illustrate it? 31. It's like a grain of mustard seed, which, when it is sown in the earth, though it is less than all the seeds that are on the earth, WEB
So it is reasonable to treat the two terms as being the same thing, and the ownership of the kingdom is actually God, and not some broader concept of the heavens.