Those are they that were sown upon the good ground. The good ground represents the heart which receives the Word of God with joy and desire, and true devotion of spirit, and which steadfastly retains it, whether in prosperity or in adversity; and so yields fruit, "sows thirty, some sixty, and some a hundredfold."
St. Jerome remarks that, as of the bad ground there were three different kinds—the way, side, the rocky, and the thorny ground; so of the good ground there is a threefold gradation indicated in the amount of its productiveness.
There are differences of conditions in the hearts both of those who believe and of these who do not believe.