“It is like a grain of mustard seed, which, when it is sown in the earth, is less than all the seeds that be in the earth:”
Mark 4:31 — Greek Interlinear
Church Fathers on Mark 4:31
Most brief indeed is the word of faith; Believe in God, and thou shalt be saved. But the preaching of it has been spread far and wide over the earth, and increased so, that the birds of heaven, that is, contemplative men, sublime in understanding and knowledge, dwell under it. For how many wise men among the Gentiles, quitting their wisdom, have found rest in the preaching of the Gospel! Its preaching then is greater than all.
Or else, that seed is very small in fear, but great when it has grown into charity, which is greater than all herbs: for 'God is love,' [1 John 4:16] whilst 'all flesh is grass.' [Isa 40:6] But the boughs which it puts forth are those of mercy and compassion, since under its shade the poor of Christ, who are meant by the living creatures of the heavens, delight to dwell.
Again, the man who sows is by many taken to mean the Saviour Himself, by others, man himself sowing in his own heart.