Basically, when you teach someone about God, if they don't have a good foundation then what you taught will not last long. Bad foundation - rocky ground. The seed (the Word) is given but does not have a place to grow and will easily wash away with rain or wind (sin). Good foundation - fertile soil. The seed falls down, grows roots and eventually the plant will flourish. It is because of the roots which were able to grow and hold the seed in place so that the rain and wind could not wash it away.
Bad foundation - rocky ground. The seed (the Word) is given but does not have a place to grow and will easily wash away with rain or wind (sin).
Good foundation - fertile soil. The seed falls down, grows roots and eventually the plant will flourish. It is because of the roots which were able to grow and hold the seed in place so that the rain and wind could not wash it away.