What is striking in what Jesus says here is that after sowing, everything carries on, on earth. The farmer just does his job and goes to sleep on time. Meanwhile, a special power works in the seed: it sprouts and grows. In the end the farmer sees the result. He himself did nothing to cause this. There are heavenly forces at work in that process of growth! God is at work, from the very beginning, with the sown Word.
27 He sleeps and rises night and day, and the seed sprouts and grows; he knows not how.