Verses 2 and 3 describe what unity is like, comparing it to oil and to dew. David's choice of these two metaphors extends the idea of "good" and "pleasant." Oil, running upon Aaron's head and down into his beard and onto his garments, was good and pleasant. It was good in the sense that it was proper and fitting for a high priest to be ordained with oil.
Our modern sensitivities may recoil at the thought of having oil poured all over us, but this oil was special, being mixed with many spices that gave it a very pleasing aroma. It was a sweet savor. In addition, it was reserved only for this one occasion, the anointing of the high priest. If one attended the anointing of the high priest, he would always associate this fragrance with that ceremony, and should he ever smell it again, it would bring back his memories of that time when a son of Aaron was raised to the rank of high priest. It was fitting, proper, and pleasant.
Why did David choose to highlight Aaron and anointing with oil? These types have a deeper connection with the unity of the brethren than simply being "good and pleasant." Aaron is the prototype high priest. Who is the antitype? Jesus Christ, our High Priest, who now sits at the right hand of God and mediates on our behalf. In the Levitical ritual, it was in the person of the high priest that at-one-ment was made with the people on the Day of Atonement. Only he could go through the veil, after his and Israel's sins had been purged, to present himself before God and sprinkle the Mercy Seat with blood. The high priest is the vehicle of that oneness—unity with God. Is this not what Jesus Christ has done? Who else has gone through the veil to bring us into unity with the Father (see Colossians 1:19-22; Hebrews 9:24-28 10:19-22)?
The picture that God trying to get us to understand is that unity comes from Him and His Son, and then down to us by His Spirit. A beautiful picture! He is the originator of unity, and without Him we cannot have unity.
It is very interesting that there has been a debate for years about how far down the oil goes. Most people take it that the word translated in the New King James as edge and in the King James as skirts means "collar." It is literally "mouth" or "opening." What is the mouth of the garment? We have two choices: On a robe, it is either the collar, which goes over the head, or the skirt hem. Many, comparing this verse with the actual ritual, say that the high priest ws anointed with just a small amount that was ceremoniously put on his head and allowed to drip down his hair and into his beard and onto his shoulders. This is probably true.
However, God may have inspired David to mean "skirt," the bottom hem down by the ankles, not the collar, because the whole of verses 2-3 is hyperbole, exaggeration. The dew of Hermon has never reached the mountains of Zion at Jerusalem; it is too far away. We must remember that the Hebrews frequently wrote in parallel units, and these verses parallel to each other. Since he exaggerates in one, he will exaggerate in the other.
He does this to get his point across to us: We are covered with oil from head to toe, and the Holy Land is covered from north to south with dew. Both oil and water are symbols of God's Spirit. It covers the whole church, every member, not just the Head. The picture here is of the fullness or completeness of the Spirit. As the High Priest's body, we are united with Him, the Head, by His Spirit.
Richard T. Ritenbaugh