the definition of "it".
I'm mindful of the hang up that folks have with this passage. It's because they read the "Kingdom of God" and confuse that as "going to heaven after one expires." And that's the mistake.
Jesus is announcing the presence of the Kingdom of God on earth as it is in heaven. Those present are Israel, yet they fail to see their calling. "It" is wisdom, and wisdom comes from God quite naturally. If wisdom permeates the culture around you (as with the people of God and his presence with them), yet one don't perceive "it", then how can "it" be given more to the one that fails to take up on it?
Matthew 13:11The Lexham English Bible
And he answered and said to them, “To you it has been granted to know the mysteries of the kingdom of heaven, but to those people it has not been granted.
- I understand the "kingdom of God" to be God's rule or reign. To enter the kingdom is to submit to Jesus as Lord (to believe and trust in him) which the leads to a life of obedience to him as one's Lord. That is the "already" part of entrance into the Kingdom--a life serving Christ in this world. The "not yet" part is what occurs at the end of the age--when kingdom subjects enter into the joy of their Lord in the eternal state.