Matthew 13:44 - The Kingdom of Heaven is like a treasure a man discovered in a field. In his excitement, he sold everything he owned to get enough money to buy the field - and get the treasure, too!
What is this "Gospel of the Kingdom"? It is the whole message of Jesus Christ. It is more demanding, more fulfilling, and more holy and more powerful than the "gospel" of typical American Christianity.
According to Jesus, when anyone finds the kingdom of God, "for joy over it he goes and sells all". Once found, it must be sought first even before necessary food and clothing; and it is such a priceless treasure that one should rather suffer the loss of a hand or eye than lose the kingdom.
Mark 9:43,47 - And if your hand causes you to sin, cut it off; it is better for you to enter life maimed than with two hands to go to hell. And if your eye causes you to sin, pluck it out; it is better for you to enter the kingdom of God with one eye than with two eyes to be thrown into hell.