[Last time we saw that the idea behind bentching where one eats is to take a place where physicality was dominant and imbue it with a realization of Hashem’s goodness. Beit Shammai said that one cannot relinquish the opportunity to do so and must even go back if he left, which is valuable for the spiritually advanced. Beit Hillel said that the average person who already left the place of physicality is better off not going back there just to make the aforementioned point.]
Gemara: There were two students: one accidentally [left the place of eating and returned] like Beit Shammai, and he found a purse of gold. The other intentionally [left the place of eating in order to bentch elsewhere] like Beit Hillel, and he was eaten by a lion.
Ein Ayah: When one returns to the place of heightened physicality for the right reasons, he is able to find the good in the physical world. The internal good is waiting there, just that it is covered in animalistic tendencies, so that its light cannot be seen. A complete person who runs his physical life according to the laws of the Torah can extract the light and purify it, just as one does to gold that is hidden among the dirt deep in the ground. When one is willing to trouble himself to go back to the place of physicality and apply the lesson, it is not just like finding gold nuggets but like finding gold that has already been processed and is now sitting securely in a purse.
Ironically, by making a mistake and having to return, he is like a sinner who repents, who can reach higher levels than a person who was always righteous. He can add personal traits including humility that others cannot. Even though it is forbidden to do the wrong thing with a plan to repent, here when he made a small mistake which he is able to fix, he actually gains more than had he remembered in the first place to bentch in the place he ate. He learns how to find the strength to actively overcome the physicality.
The person who intentionally "followed Beit Hillel" by not bothering to bentch where he ate (Beit Hillel only allowed him not to return, not to leave of his own volition) felt that it is proper to distance oneself as soon as possible. He thought that it was better for Birkat Hamazon to be done without mixing in any physical elements. Therefore, he did not learn how to stand up against the world of physicality and tame it with sanctity. This is signified by being eaten by a lion, in other words, not being able to stand up to a physical temptation when it struck with all its power.
It is within the realm of what is philosophically plausible that events that can teach a moral lesson for the entire nation will occur [in a manner that seems exaggerated for the specific people to whom they happened. In other words, one student did not deserve the gold, and the other did not deserve death.]. These events taught people the proper approach that they should take. The appropriateness of the response is in that vicious animals attack man only if the victim appears to the attacker like an animal (Shabbat 151b). The similarity to an animal is in the internal characteristics. When one learns how to have ethics and fear of Hashem, it implants in him the stamp of a human. Such a person may then be able to [find gold and] fulfill the Torah within a life of riches. Even as he has more material possessions, that person will keep his divine form, and a lion will leave him alone. He will enjoy this world and the next and will use his riches to make the world a more complete place.