Since this parable supplements the parable of the soils, it appears that Jesus addressed it to the multitudes (cf. vv. 1-9). Mark is the only evangelist who recorded this part of the discourse. Each parable to the multitudes illuminated an aspect of the messianic kingdom.
The identity of the man in the parable is secondary, though in view of the former parable he represents Jesus and His disciples. The significant element is how the seed grows. In the former parable the seed represented the good news about the kingdom, and it means the same thing here.
The seed enters into the ground and grows mysteriously, without the continuing work of the sower. God causes it to grow. Farmers know the conditions that help or hinder plant growth, but they do not fully understand the growth process nor can they cause growth. Only God can do that. The earth itself appears to cause plants to grow automatically as they move through the various stages from germination to maturity. Jesus stressed this fact by putting the Greek word automate("by itself") in the emphatic first position in the sentence. Finally the sower, who had played no visible role in the growth of the crop, returned to the field as its reaper.
This parable would have encouraged the disciples to realize that the preaching of Jesus and their own preaching in anticipation of the kingdom would bear fruit in time. God would cause the seed that they planted in the ears and minds of many to germinate into new life and to grow. Growth of the believing community would increase, though no one could really explain why it was growing except that God was responsible for it (cf. Matt. 16:18). Eventually there would be a harvest of the crop when God, the ultimate sower, saw that the time was right. Probably this refers to the end of the messianic kingdom. The parable bridges history from the initial time of sowing in Jesus' day culminating in the harvest at the end of the messianic (millennial) kingdom.
Another interpretation of this parable views it as describing growth within individual believers.112The problem with this view is the identity of the kingdom of God. Other interpreters see it as picturing the mysterious appearing of the messianic kingdom at the time of harvest.113However the emphasis in the parable is on the growth of the seed, not the harvest of the crop. A third view takes the period of growth to be the inter-advent age with the harvest occurring when Jesus returns to establish His kingdom on earth.114This view limits the parable to the "mystery form"of the kingdom. I find nothing in the text to justify interpreting the kingdom as the Old Testament predicted it as the mystery form of the kingdom. I believe that when Jesus said the kingdom of heaven (or God) was similar to something what He described included the messianic (millennial) kingdom. It did not just represent the inter-advent age leading up to its beginning.