Note 2 at Lu 8:11: This parable is illustrating the importance of the Word of God. God's Word contains total power (Ps 138:2 and Heb 1:3), but it has to be planted in our hearts and allowed to germinate before it releases that power.

The seed is God's Word, and the types of ground are the four major categories of people's hearts ("sown in his heart" - Mt 13:19, also see Mr 4:15). The Word was the same in each situation (an incorruptible seed - 1Pe 1:23), but there were different results in each case because of the condition of people's hearts, not because of the Word. The Word doesn't work for everyone, because not everyone will allow the Word to work. The variable in this parable is the condition of these hearts. God's Word is always the same. It has the same potential in every heart.