Charles Ellicott Commentary Mark 4:27

"and should sleep and rise night and day, and the seed should spring up and grow, he knoweth not how." — Mark 4:27 (ASV)

And should sleep, and rise.—So it was in the world’s history. Men did not know the greatness of the new force that had been brought into action. Philosophers and statesmen ignored it. Even the very preachers of the new faith, the “sowers” of the parable, were hardly conscious of the enormous revolution which they were working.

So it is in the individual life. The seemingly chance word, the new truth that flashes on the soul as a revelation, the old words now for the first time apprehended in their true force, these prove to be the seeds of a new growth in the soul.