The Parable of the Hidden Treasure – Matthew 13:44
The kingdom of heaven is like a treasure hidden in the field, which a man found and hid; and from joy over it he goes and sells all he has, and buys that field.
A study of the Mt. 13 kingdom parables is a fascination study. The characters remain the same throughout the various parables. Jesus is the "man". The world is the field. The treasure is Israel which is in the world.
In order for Jesus to finally receive his throne in Israel, the one promised to him, he had to buy the whole world with everything he had... his life to get it. Once that was done, the kingdom existed in a mystery form in the hearts of believers.... a place not at first discernible, hidden in the "earth".
Later, when Jesus returns, the kingdom will be visible, tangible, in Israel with Jesus sitting on the throne of David.
During the church age, or since the days of the apostles, Christians teach a gospel of reconciliation. The gospel of the kingdom will be preached by Israel (144K male virgins) during the great tribulation after the church has be evacuated. It is an Israeli message, whereas the gospel of reconciliation is a directed to "whosoever".