The Kingdom of God Defined

Definition
"The heavens is a place where God dwells." (Alma 18:30) Heaven is the place where God is King and therefore, is called His kingdom. The kingdom of God has two locations, in heaven and on earth. In heaven it is called the kingdom of heaven and on earth it is called The Church of Jesus Christ of Latter-day Saints. The kingdom of God on earth currently has limitations while the kingdom of God in heaven does not but is all encompassing. Jesus calls it the kingdom of My Father or My Father's house which is a name also given to the temple.

In support of this definition, Wilford Woodruff said, "By the united efforts, alone, of the Saints of God, in this last dispensation, the building up of Zion will be effected, and the kingdom of God on earth, be prepared for a union with the kingdom of God in heaven; and thus shall the chain which has bound together in one the hosts of heaven, extend and grasp in its circumference all who have been obedient to the mandates of God." (“Union,” Millennial Star, November 15, 1845, 168., See also Jesus the Christ Ch 42)

Many Mansions
Jesus in his mortal ministry said, "In my Father’s house are many mansions: if it were not so, I would have told you. I go to prepare a place for you." (John 14:2) There are more than ten scriptures that talk about mansions:
Thou hast prepared a house for man, yea, even among the mansions of thy Father (Ether 12:32)
That place which thou hast prepared in the mansions of thy Father (Ether 12:34)
There is a place prepared for you in the mansions of my Father (Enos 1:27)
In my Father’s house are many mansions ...  I go to prepare a place for you (John 14:2)
In the mansions of my Father, which I have prepared for them (D&C 59:2)
The mansions prepared for him of my father (D&C 72:4)
In the mansions which are prepared (D&C 76:111)
The mansions which I have prepared in the house of my father (D&C 81:6)
In my Father’s house are many mansions, and I have prepared a place for you; (D&C 98:18)
I have prepared a crown for him in the mansions of my father (D&C 106:8)
In the place which I have prepared in the mansions of my Father (D&C 135:5)

Kingdoms of Salvation
Joseph Smith said, "It appeared self-evident ... that if God rewarded every one according to the deeds done in the body the term ‘Heaven,’ as intended for the Saints’ eternal home, must include more kingdoms than one." In Doctrine and Covenants we learn that in heaven there are three kingdoms, also called kingdoms of glory or kingdoms of salvation. These kingdoms are called the telestial, terrestrial and celestial kingdoms. We learn that "the glory of the celestial is one, even as the glory of the sun is one. And the glory of the terrestrial is one, even as the glory of the moon is one. And the glory of the telestial is one, even as the glory of the stars is one; for as one star differs from another star in glory, even so differs one from another in glory in the telestial world;" (D&C 76:96-98) We also learn that "In the celestial glory there are three heavens or degrees." (D&C 131:1)

It has been assumed by some that the kingdom of God or the kingdom of heaven is exclusively the celestial kingdom. This is the kingdom where God dwells, God the Father, God the Son and God the Holy Ghost. This seems to make sense, except that the terrestrial kingdom enjoys the presence of God the Son and God the Holy Ghost and the telestial kingdom enjoys the presence of God the Holy Ghost, are the servants of God and heirs of salvation. All three kingdoms receive glory from God; a fullness or a portion of His glory. To say that the telestial kingdom is not included in the kingdom of God, is equivalent to saying that God the Holy Ghost is not God or that those in the telestial kingdom do not enjoy the presence and glory of God, even that of the Holy Ghost.

The Church of Jesus Christ of Latter-day Saints is the kingdom of God on earth, but neither the Father nor the Son dwell on earth. However, all members of the church are given the gift of God the Holy Ghost. We have entered into His kingdom on earth at the entry level which is a telestial level. This is supported by the symbolism of the temple, including the temple of Solomon, as well as what is learned there.

How then can the kingdom of God be exclusively the celestial kingdom? The answer is that it is not. In reference to the revelation given in D&C 76, where we learn about three kingdoms of God's glory Joseph Smith said, "Heaven ... must include more kingdoms than one." Why would God give glory to anyone outside of His kingdom? The answer is that He would not. Just because God the Father does not dwell in the telestial kingdom does not mean that it is not part of His kingdom.

Analogy
I have given an appropriate analogy for this in a previous blog post:
A man owns a house with one door into the house. The door leads directly onto the first floor of the house, which has three floors with stairs connecting them. The man lives on the third, highest floor. If the man told someone that they had to enter the door to get into his house, they may think, having never seen the house, that there is only one floor to the house. Now, if the man showed someone pictures of the house and talked about the differences between each floor, they may think that there are actually three houses because of how different the floors are. For example, when he talked about the third floor it may be interpreted as the floor of the third house and the door into his house only goes to the floor of the third house, which is the floor where he lives.

Here is the equivalent: God, the Godhead, owns a house with one door into the house, baptism. Baptism leads directly into the telestial kingdom of the kingdom of God, which has three kingdoms with ordinances allowing for progression to higher kingdoms while men are in the probationary state. All members of the Godhead live in the celestial kingdom, the highest kingdom. The terrestrial kingdom enjoys the presence of Christ and the telestial kingdom enjoys the presence of the Holy Ghost. The three kingdoms are one kingdom just as the three members of the Godhead are one God.