Genesis 49:17

The fact that the prophet says "biting the heel of the horse" signifies that Christ will test those who announce the way of the truth and salvation. So he also tested the apostles, cheated Judas and took hold of him; he took hold of him as of a horse and threw the rider who was on it to death.

The path indicates a more narrow way, which demonstrates that he does not walk along that wide and spacious way leading to death but along that narrow way full of obstacles leading to life. He bites the heel of the horse and so does what the apostle Paul said: "I pommel my body and subdue it, lest after preaching to others I myself should be disqualified." He acts in this manner so that the rider may fall backwards. He always fears elations and heights and prefers his soul to fall from an evil height to an honest humility, in order to learn from Christ, who is modest and gentle in his heart. It is typical of those who progress to fear elation. And finally a very important apostle like Paul said, "A thorn was given me in the flesh, a messenger of Satan, to keep me from being too elated." And so the soul, after being recalled from elation and led back to the humility of Christ, waits for the salvation of the Lord.

Therefore, when we are going well on the road, let us beware that a snake does not hide in the path and overthrow the footprint of the horse, that is, of our body, and suddenly cast down the sleeping rider. For if we are watchful, we ought to be somewhat cautious and to avoid the bites of the serpent. Therefore, let not the sleep of negligence oppress us, the sleep of the world, let not the sleep of riches oppress us; lest it also be said of us: They have slept their sleep, and all the men of riches have found nothing. But there are also sleeping knights, of whom it is written: Those who mounted the horses fell asleep. If greed wounds your heart, if lust inflames it, you sleep, knight, and therefore you cannot control your body, that is, your horse. Therefore, stay awake, so that even if you fall, that is, if you die, you do not fall asleep. For those who fall asleep in their sleep, find nothing. But you, wait for salvation from the Lord, look to the coming, so that you may find the grace of resurrection. Judas was sleeping: finally, he did not hear the words of Christ. Judas was sleeping, and indeed the sleep of riches, seeking a reward for his betrayal. The devil saw him sleeping, and oppressed by the heavy sleep of greed: he entered into his heart, wounded the horse, threw off the rider, whom he separated from Christ.