Mark 4:26

And He said, So is the kingdom of God, as if a man should cast seed into the earth. This is another parable, different from that of the Sower, which precedes it. Both, however, are taken from seed, but differently applied and explained. Moreover, by the seed, as SS. Chrysostom and Bede rightly explain, both here and in S. Matthew 13, is signified evangelical doctrine. By the field, hearers; by the harvest, the end of the world, or each one's death, is meant. Ver. 27. And should sleep, that is to say, the sower, and rise, night and day, and the seed should spring and grow up whilst he knoweth not. Some refer the words rise night and day to the seed; meaning that the seed should germinate, it knoweth not how, that is, like a man sleeping. More obviously, S. Chrysostom, Theophylact, Maldonatus, and others refer the words to the sower, so that night pertains to the word sleep, day to the word rise. The meaning is, As the husbandman who has sowed is sleeping idly in the night, and is employed in various occupations during the day, and thinks not about the seed, that seed is germinating by its own innate force, and is growing up whilst the husbandman knoweth it not. So also it puts forth first the blade, then the ear, and then the full corn in the ear. So, too, in the same manner is the doctrine and preaching of the Gospel. They were sown by Christ and His Apostles, that is, they were preached from small beginnings. But by degrees they grew insensibly into the mature and mighty harvests of the faithful, whilst Christ was, as it were, sleeping in heaven, and permitting the Jews and unbelieving nations and tyrants to rise up against His Apostles, and persecute and kill them. It increases, I say, and propagates itself gradually, until it fills the world, when, the harvest being ripe, the corn, i.e., the elect, shall be gathered into the granary of heaven.

By this parable, then, is signified the power of the Gospel, which by degrees has pervaded the whole world, and is converting it to Christ. Tacitly, also, it is signified that preachers of the Gospel must not glory in their preaching, as though they by it were converting the world. For, as the Apostle saith, "Neither he that planteth is anything, nor he that watereth, but God that giveth the increase (1Co 3:7). Christ further intimates that preachers ought not to be downcast if they see small and tardy fruits of their preaching, because God will, by the few converted by them, gradually convert many more. So S. James, by means of seven, or, as some say, by nine, whom he converted in Spain, converted the whole country.