Both the Son of Man and the devil are battling and contending for the space of the earth. The means by which they seek to affect and control space is with humans, either good seeds (sons of the kingdom) or bad weeds (sons of the evil one). In the parable, it is more explicit than the other parables that the seeds are human beings. Matthew and Jesus, through the parable, are affirming that the structure of a place is changed socially. Notice that Matthew follows the use of good soil (13:23) with good