His most constant subject, and the one he never defines.
The kingdom of God is the thing Jesus talks about most. It is also the thing he never once explains directly. Asked what it is, he answers with a farmer, a merchant, a woman with flour, a man who finds something in a field.
That is not evasion. The comparisons are the teaching, and they have a shape in common.
the Kingdom of Heaven is like treasure hidden in the field, which a man found, and hid. In his joy, he goes and sells all that he has, and buys that field.
Spoken to a crowd by a lake, in a run of comparisons delivered one after another. The detail that carries it is three words long: he sells everything in his joy. Not out of duty, and not after weighing it up. The price is total and the man is delighted, which tells you what he thinks he has found.
They are small, and they are hidden. A seed, some yeast, something buried in a field, something growing while nobody watches. None of them is an institution and none arrives with an announcement — which is the explicit point of Luke 17:20.
And every one of them is worth more than it looks. The man sells everything; the merchant sells everything; the seed becomes the largest plant in the garden. The teaching is consistently that this thing is easy to walk past and costs whatever you have.
Walking with Jesus: Devotional has a collection called Teachings of the Kingdom that walks these one a day, each with the moment it was spoken in, a reflection, a prayer and one thing to carry into the day.
A one-time purchase, about five minutes a morning.