There has been much debate over what the Lord meant by the Kingdom. The primary cause being the fact that neither Jesus nor the Gospel writers explicitly defined it. It was something that they assumed would be understood. For both, the Greeks and Jews define “kingdom” as the abstract concept of one’s “sovereignty, royal power, or authoritative rule”.
In 1 Chronicles, we read how Saul’s kingdom was turned over to David, indicating that the authority that was once Saul’s was now David’s. David then had legal authority. He was king. (See 1 Chronicles 12:23) The nobleman went to the governing authority in a far country to receive his rite to be a governing authority. (See Luke 19:12) But a “kingdom” was also, a concrete concept, “a territory, people, or realm over which a king rules”. (See 2 Chronicles 20:30; Matthew 4:8)
With this understanding, you come to see the Kingdom as something that is both present and future, as well as spiritual and physical. The Kingdom is now but not yet. It is as Baker’s Encyclopedia of the Bible defines it,
The sovereign rule of God, initiated by Christ’s earthly ministry and to be consummated when “the kingdom of the world has become the kingdom of our Lord and of his Christ” (Rv 11:15).[i]
This is why Jesus could both point to a present and spiritual kingdom, but also a future and physical kingdom.
[i] Ladd, G. E. (1988). Kingdom of God (Heaven). In Baker encyclopedia of the Bible (Vol. 2, p. 1269). Grand Rapids, MI: Baker Book House.