Hi Kweli,
kingdom - a realm or region in which something or someone is dominant. (Merriam-Webster)
kingdom - The inhabitants or population subject to a king. (Webster)
Well in Luke 17:21 where it says "the Kingdom of God is within you." I believe "the Kingdom of God" is Jesus Christ. The Elect, subjects of His domain, are being added to the kingdom through the Holy Spirit living in them. Just as Christ and the Father are 'one,' the Elect are being made into that same image, becoming 'one' with them, forming the kingdom.
1Co 3:16 Do you not know that you are the temple of God and that the Spirit of God dwells in you?
Col 1:27 To them God willed to make known what are the riches of the glory of this mystery among the Gentiles: which is Christ in you, the hope of glory.
So right now "the Kingdom of God is at hand" because God is preparing His Elect, those few who receive the Holy Spirit - kingdom now.
All the parables refer to this few being chosen now to be prepared to reign with Christ.
Mar 4:26 And He said, "The kingdom of God is as if a man should scatter seed on the ground,
This parable is speaking of the Elect, it shows of those who receive the Truth, so few bear fruit, but this is the kingdom.
Mat 13:31 Another parable He put forth to them, saying: "The kingdom of heaven is like a mustard seed, which a man took and sowed in his field,
v. 32 which indeed is the least of all the seeds; but when it is grown it is greater than the herbs and becomes a tree, so that the birds of the air come and nest in its branches."
This parable shows how the kingdom starts tiny, with the first converts, the Apostles. But Christ is bringing more into His kingdom everytime He opens the eyes of one of His Elect.
So the Kingdom is Christ and the Elect. Right now the Kingdom is within the Elect, because it is not manifested to the world yet.
John 14:22 Judas (not Iscariot) said to Him, "Lord, how is it that You will manifest Yourself to us, and not to the world?"
v. 23 Jesus answered and said to him, "If anyone loves Me, he will keep My word; and My Father will love him, and We will come to him and make Our home with him.
When He comes to rule and reign, the Elect will be with Him and His Kingdom will be revealed and reign over the world.
1Tim 6:13 I urge you in the sight of God who gives life to all things, and before Christ Jesus who witnessed the good confession before Pontius Pilate,
v. 14 that you keep this commandment without spot, blameless until our Lord Jesus Christ's appearing,
v. 15 which He will manifest in His own time, He who is the blessed and only Potentate, the King of kings and Lord of lords,
v. 16 who alone has immortality, dwelling in unapproachable light, whom no man has seen or can see, to whom be honor and everlasting power. Amen.
Rev 1:5 and from Jesus Christ, the faithful witness, the firstborn from the dead, and the ruler over the kings of the earth. To Him who loved us and washed us from our sins in His own blood,
v. 6 and has made us kings and priests to His God and Father, to Him be glory and dominion forever and ever. Amen.
v. 7 Behold, He is coming with clouds, and every eye will see Him, even they who pierced Him. And all the tribes of the earth will mourn because of Him. Even so, Amen.
This is how I understand this, I hope this is of some help.
mercy, peace and love
Kat