The parable of the sower and the seed is very important because it is the basis for understanding all the other parables (Mk 4:13) as well as understanding God's kingdom, which is revealed in parables (see Mt 13:24-50). This parable is not about the sower and the seed, but about four conditions of ground. These represent our openness or lack of openness to God's word (Mk 4:20). It is difficult to take God's word to heart because God's ways are not our ways (Is 55:8). Our hearts are naturally deceitful (Jer 17:9) and hardened (see Ps 95:8), and the Lord repeatedly challenges us in His word to repent.
In addition to all these difficulties, we have special problems in taking God's word to heart in a large group setting. When Jesus taught the parable of the sower, seed, and the grounds, He was sitting in a boat on the water a few feet from the shore and addressing "a huge crowd" (Mk 4:1). Jesus was using the water both for crowd-control and as a medium to project His voice to the masses. He was using a primitive form of mass media. In this context, we tend not to take God's word personally. We sit passively waiting to be entertained and look around at the others in the crowd.
This dangerous setting for hearing or not hearing God's word is the setting in which we usually hear the word. When attending Sunday Mass, reading books, watching videos, listening to the radio, and looking at a computer screen, watch out! You are in imminent danger of not taking God's word to heart. "Let him who has ears to hear Me, hear!" (Mk 4:9)