Mark 4:26
He said, "The Kingdom of God is as if a man should cast seed on the earth,
WEB
And he said, So is the kingdom of God, as if a man should cast seed into the ground;
KJV
What Mark 4:26 means
Jesus likens God's kingdom to a farmer who plants seed and then goes on with ordinary life, sleeping and waking, while the seed grows on its own by a power he neither controls nor understands.
This short parable appears only in Mark, tucked inside a run of seed parables in chapter 4, between the sower and the mustard seed. It answers a question the sower parable raises. If the word is scattered like seed, who makes it grow? Jesus's reply is that the growth is not the farmer's doing at all.
The first hearers were mostly rural people in Galilee who knew the strange helplessness that follows planting. You break the ground, you sow, and then you wait through nights and days you cannot hurry along. Jesus says the kingdom of God arrives in that same manner, real and unstoppable, coming up without being manufactured by human effort.
The wording is precise. In the next verse the ground "bears fruit" through the Greek automatē, the root behind our word automatic, meaning of itself, spontaneously. And the phrase "he doesn't know how" is not an ignorance waiting to be fixed. It names the proper posture of a person standing in front of growth they did not cause and cannot fully explain.