Although sibling rivalry is common, it can be quite puzzling upon further reflection.
Generally speaking, siblings would come from the same parents, and since they may grow up together, it may be presumed that the siblings would think and feel alike.
But obviously that is not necessarily true, and often sibling rivalry can be even quite bitter.
In the 1st reading, we heard of a case of sibling rivalry as Miriam and Aaron spoke against Moses in connection with the Cushite he had married.
But that was rather a superficial matter as the real issue was Miriam and Aaron questioned if the Lord had spoken to Moses only.
They argued that the Lord has spoken to them too. But the real issue was pride has gotten into them and they were actually challenging the authority of Moses.
So the Lord summoned the three of them and He attested that He gave the authority to Moses, and because they were arrogant enough to challenge Moses, hence Miriam was punished, while Aaron begged for mercy.
This reminds us that whether in a family, or community, or ministry, or organisation, there will be some who are appointed to leadership roles to serve with humility.
Respect for the appointment and authority must be given so that there can be unity.
Rivalry is a product of pride. Let us be humble and respectful to each other so that we will grow together in charity.