The Kingdom of God has double meaning: one ethical or spiritual and another theological. In the Gospel of John there are seven affirmations of the "I am", one of these affirmations is: "I am the good shepherd", John 10:11. These affirmations of the "I am" represent the divinity of Jesus and constitute the theological aspect of the Kingdom, that is, the son coexisting with the Father and the Holy Spirit.
Jesus teach us that he is the shepherd who cares and guide his sheeps. Christ in his figure of good shepherd personifies God's guidance. The guidance of God is an aspect of the eternal life.
Even if in the Gospel of John the eternal life is defined as the knowledge of God: This is eternal life that you know the only true god, John 17: 3. This knowledge is not presented alone, along with knowledge there is a set of blessings: longevity, happiness of heart.
We can extend the definition of eternal life and say that  the eternal life are blessings that God gives in advancement of the life in glory (afterlife), and among these blessings is God's guidance.The Eternal life is the angelic gift by excellence, that is, the gift that makes us participate in the life of the angels, they (the angels) are created with the same knowledge of God.
Christ personifies the eternal life, and not only that, Christ personifies the spiritual gifts and divine attributes of God. Christ is "Son of Man".
The Kingdom of God is the man who seeks God's Mercy, that is to say the man who is "son of God" and the other way is the Mercy of God that is personified in Christ, is God who is "Son of Man".
The Kingdom of God has a double meaning: it is a round trip, the going is ethics, the return is theology (Father, son, holy spirit).
Christ as the personification of God's guidance teach us to live in the culture of the excellence, in the culture of the Kingdom of God, "be perfect as the heavenly Father is perfect" Matthew 5:21, "Be holy because I am holy" 1 Peter 1:16.
Christ calls us to live the perfections ( spiritual gifts) of God, he calls us to be "sons of God" as he is "son of man".