Aside from acting as a protection amulet, the will could also act as family insurance.
An ancient king would often be worried that his heir would be a fatuous and self-indulgent ruler that would throw away all of the country’s blessings, without leaving any blessings behind for the future generations.
As for the modern wealthy men, they would also be afraid that their heirs would end up becoming prodigal sons and ultimately ruin the family inheritance.
Therefore, almost every wealthy man woul