Matthew 13:4

But those things which He silently left to our understanding, should be shortly noticed. The wayside is the mind trodden and hardened by the continual passage of evil thoughts; the rock, the hardness of the self-willed mind; the good soil, the gentleness of the obedient mind, the sun, the heat of a raging persecution. The depth of soil, is the honesty of a mind trained by heavenly discipline. But in thus expounding them we should add, that the same things are not always put in one and the same allegorical signification.

(Version 4.) Behold, he who sows went out to sow. And while he was sowing, he was inside, at home, speaking to the disciples the mysteries. Therefore, he who sows the word of God went out from his house, in order to sow in the crowds. But this sower who sows is signified to be the Son of God, and to sow the word of the Father among the people. And at the same time, observe that this is the first parable, which is placed with its interpretation. And beware that wherever the Lord explains his words and is asked by the disciples to explain inwardly, we should not want to understand anything else, or anything more, or anything less, than what was explained by him.

Let us look, as from a broader perspective, at what it means to be on the road. In a way, every road is hardened and foolish on account of the fact that it lies beneath everyone's feet. No kind of seed finds there enough depth of soil for a covering. Instead, it lies on the surface and is ready to be snatched up by the birds that come by. Therefore those who have in themselves a mind hardened and, as it were, packed tight do not receive the divine seed but become a well-trodden way for the unclean spirits. These are what is here meant by "the birds of the heaven." But "heaven" we understand to mean this air, in which the spirits of wickedness move about, by whom, again, the good seed is snatched up and destroyed.