There are two constants in this story—the seed and the sower. There is one variable—the soil. The soil represents our hearts. The seed represents truth. The sower is God himself.
Soil must be soft, deep and free from clutter in order for growth to occur. Our hearts must be soft to truth. Our hearts must be able to withstand difficulties and maintain our faith. Our hearts must be free from the cares of the world.
With soft, deep and uncluttered hearts, there can be so much growth that we become sowers of seed ourselves.