Mark 4:5

(ubi sup.) It goes on: And some fell on stony ground. He calls stone, the hardness of a wanton mind; He calls ground, the inconstancy of a soul in its obedience; and sun, the heat of a raging persecution. Therefore the depth of earth, which ought to have received the seed of God, is the honesty of a mind trained in heavenly discipline, and regularly brought up in obedience to the Divine words. But the stony places, which have no strength for fixing the root firmly, are those breasts which are delighted only with the sweetness of the word which they hear, and for a time with the heavenly promises, but in a season of temptation fall away, for there is too little of healthful desire in them to conceive the seed of life.

But some fell upon rocky places, where it had not much earth; and it immediately sprang up, because it had no depth of earth. And when the sun was risen, it was scorched; and because it had no root, it withered away. And the Lord explains the mystery of this seed. In this exposition, we learn that these things are not always allegorically placed in the same significance. For stone indicates the hardness of a stubborn mind, earth the gentleness of an obedient soul, and the sun the fervor of a raging persecution; although elsewhere he places the sun in a good light, saying the righteous will shine in the future like the sun in the kingdom of their Father. And in the construction of the spiritual house, he teaches that digging deep, earth must be removed, and stone laid in the foundation, that is, the earthly thoughts are to be cleansed from the innermost recess of the heart, and the strength of invincible faith to be laid in the foundation of good works. In this instance, the depth of earth properly cultivated should have received the seed of the word, the uprightness of a soul exercised in heavenly disciplines and regularly trained in listening and obeying divine words. But rocky places, covered with thin soil, can quickly germinate the received seed, yet do not have the strength to set roots; these are, without a doubt, hearts untrained in the studies of discipline, softened by no trials of temptation, delighted only for a moment by the sweetness of the heard word and celestial promises, but fall away in time of temptation; for when they present the fleeting sweetness of the heavenly oracle to their inherent austerity, as if a place designated for the holy seed, they cover a great heap of stones with a thin layer of soil. Therefore, they cannot reach the fruit of righteousness because of the little amount of saving desire inherent in them to conceive the seed of life, and the abundance of harmful hardness that obstructs the fruit of salvation.