I have always found Psalm 133 a little strange. What does "It is like the precious oil ... upon ... Aaron's beard" got to do with "See how good and how pleasant it is for brothers to dwell together in unity"? None of the commentaries really satisfied my curiosity regarding this unusual juxtaposition.
Then I thought about brothers in the Bible and how seldom they related to one another in love. Moses and Aaron served God together for 40 years. I am not aware of any other such connection between brothers in the Bible. On the contrary, the relationships between brothers were often acrimonious.
The very first man born of a woman murdered his brother (Genesis 4:8). When God found a man with whom he could start a nation, his eldest son had to leave home while in his teens (Genesis 21:9-14). Jacob feared for his life because of his twin brother (Genesis 27:41). Jacob's sons came very close to killing their brother, but sold him into slavery instead (Genesis 37:18, 28).
Psalm 133 was written by David. His brothers did not treat him kindly when he went to bring them food while they were at the battle front (1 Samuel 17:28). But his greatest heartache must have been the toxic relationships among his sons. Absalom killed Amnon because he had raped his sister (2 Samuel 13:28). Even Solomon put one of his brothers to death because he had made a grab for the throne (1 Kings 1:5; 2:25).
On which relationships David was reflecting we can only wonder. But he must have found comfort in reading about Moses and Aaron, even though their relationship had also gone through an unhealthy patch (Numbers 12:1).
