The right side of the brain, the inner child that must be brought forth in meditation, is exactly what the aging self clenches against sending down into the lower mind. Benjamin, the son of the right hand, is the awakened right hemisphere, and the refusal to let him go is the pride and fear of a person unwilling to release that child into the region of bondage where the emotions and the carnal self rule.
The brother already lost to that darkness, and the gray hairs threatened with the grave, are the mind convinced that surrender means only death and never return. So the higher part is held back and kept from its work. What speaks here is the self gripping its last treasure, sure that to let it descend is to lose it for good.
Benjamin the son: the son of the right hand, the awakened right hemisphere and the inner child drawn out in meditation
The grave: the descent into Egypt and matter, bondage to the lower mind and the emotions where the higher part fears to go
Gray hairs: the aging self worn down by fear, certain that letting go means loss