Gregory the Great
Catena Aurea · Markusevangelium 4
And he said, So is the kingdom of God, as if a man should cast seed into the ground; And should sleep, and rise night and day, and the seed should spring and grow up, he knoweth not how. For the earth bringeth forth fruit of herself; first the blade, then the ear, after that the full corn in the ear. But when the fruit is brought forth, immediately he putteth in the sickle, because the harvest is come.
(in Ezech. 2. Hom. 3) Or else; Man casts seed into the ground, when he places a good intention in his heart; and he sleeps, when he already rests in the hope which attends on a good work. But he rises night and day, because he advances amidst prosperity and adversity, though he knows it not, for he is as yet unable to measure his increase, and yet virtue, once conceived, goes on increasing. When therefore we conceive good desires, we put seed into the ground; when we begin to work rightly, we are the blade. When we increase to the perfection of good works, we arrive at the ear; when we are firmly fixed in the perfection of the same working, we already put forth the full corn in the ear.