In just three verses, David emphasizes something that is too often forgotten in Christendom: how much God wants us to get along with one another. Like the anointing of Aaron, unity among brethren brings God’s approval. Like the refreshing dews of Mt. Hermon, Israel’s highest mountain, unity brings God’s refreshing blessing.
When brethren treat one another like anything but family – even (and perhaps especially) in the name of orthodoxy (or truth) – they fall outside God’s approval and blessing. It is possible to be right, and act wrong, but it is not possible to act wrong and be like God.