Mark 4:26

(Vict. Ant. e Cat. in Marc.) A parable occurred, a little above, about the three seeds which perished in various ways, and the one which was saved; in which last He also shows three differences, according to the proportion of faith and practice. Here, however, He puts forth a parable concerning those only who are saved. Wherefore it is said, And he said, So is the kingdom of God, as if a man should cast seed into the ground, &c. (Vict. Ant. e Cat. in Marc.) Or else He calls by the name of kingdom of God, faith in Him, and in the economy of His Incarnation; which kingdom indeed is as if a man should throw seed. For He Himself being God and the Son of God, having without change been made man, has cast seed upon the earth, that is, He has enlightened the whole world by the word of divine knowledge.

(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.

The kingdom of God is the Church, which is ruled by God, and herself rules over men, and treads down the powers which are contrary to her, and all wickedness.