In verse one of Psalm 133, David talked about brethren dwelling together in unity in order to establish a physical basis for community. In verse two of Psalm 133, David explains how unity works from a spiritual perspective. David said, “It is like the precious ointment upon the head, that ran down upon the beard, even Aaron’s beard: that went down to the skirts of his garments.
When Aaron became the chief priest, his head was anointed with oil as a sign of his consecration to God (Leviticus 8:12). Aaron was the spiritual leader of Israel and was a direct representative of God that lived among the Israelites to remind them of God’s presence in their community. David’s expression of Aaron’s anointing being like brethren dwelling together in unity is intended to convey the point that God’s presence in the community was the source of its unity or what kept the people united.
The oil that was used to anoint Aaron was a combination of olive oil and sweet smelling spices that when combined formed a strong perfume that could probably be smelled from a great distance. The idea behind the anointing was the goodness of God being like a sweet smelling fragrance that affected everyone that came in contact with it.
Paul talks about the unity of the Spirit in Ephesians chapter four. Paul encouraged believers in the city of Ephesus “to keep the unity of the Spirit in the bond of peace…Till we all come in the unity of faith, and the knowledge of the Son of God, unto a perfect man, unto the measure of the stature of the fullness of Christ” (Ephesians 4:3,13). Paul’s reference to the measure of the stature of the fullness of Christ appears to be tied to the anointing of the priests and could clarify why David used the anointing of Aaron as an example of unity.
If you think of the priests’ garments as a representation of God’s holiness imparted to man, the anointing oil running down onto the garments was a picture of Jesus’ death as the atonement for sin. The anointing of the priest was an act of faith that linked him to the death, burial, and resurrection of Christ. David used this illustration to make the point that the brethren dwelling together in unity during his reign was based on an act of faith. They all believed they were establishing the kingdom of Christ and that one day he would walk in their midst and his presence would affect everyone that came in contact with him.