This parable about the seeds is so familiar that I never realized it is only found in Mark. Of course we have all heard interpretations of the many meanings within it but I haven't ever heard this one by St. Gregory the Great.
An agricultural parable found only in Mark. Jesus compares the mystery of natural, organic growth to the expansion of the kingdom of God. The kingdom will visibly mature like grain, but the spiritual forces behind it will remain invisible. The parable of the Leaven in MT 13:33 elucidates the same mystery.A note for reflection adds what we already know about this parable's larger meaning, but what is good for me to remember.
Morally (St. Gregory the Great, Hom. in Ezek 2, 3), the maturing grain signifies our increase in virtue. First, the seeds of good intentions are sown; these gradually bring forth the blade of repentance and ultimately the mature ear of charitable works. When established in virtue, we are made ripe for God's harvest.
The Gospel of Mark
(The Ignatius Catholic Study Bible)
Despite the many seeds apparently sown in vain, God is at work to produce what will finally be revealed as a stupendous harvest. The parable illustrates the "mystery of the kingdom" that Jesus mentioned in 4:11. The reign of God will not come about through unmitigated success and uninterrupted growth. An unexpected but necessary part of the plan is the setbacks and failures that give Jesus' disciples a share in the mystery of his own suffering.