Psalm 133:1-3 (NKJV), "Behold, how good and how pleasant it is for brethren to dwell together in unity! It is like the precious oil upon the head, running down on the beard, the beard of Aaron, running down on the edge of his garments. It is like the dew of Hermon, Descending upon the mountains of Zion; For there the LORD commanded the blessing–Life forevermore."
?When Aaron was anointed as the high priest in Israel, the holy anointing oil was poured only upon his head. The under-priests were not anointed individually. They were recognized as members of the High Priest's body. This was a picture of The Christ, head (Jesus) and body (spirit-begotten Christians), receiving the anointing of the Holy Spirit. Jesus received the Holy Spirit at His baptism and the church (as one body) received it at Pentecost. Colossians 1:27, "…Christ (anointing) in you, the hope of glory."
Oil reduces friction and increases smooth cooperation. So the evidences that one has been anointed with the Holy Spirit include a desire to assist others to see and to grow in knowledge and Heavenly grace. The anointing helps us to develop the mind of Christ – the disposition which is loving, generous, forgiving toward others and which is reverential toward God and obedient to His will. Whoever finds, on self-examination, that he has these evidences in his own heart has the witness of the Spirit that he is a child of God.
The most favorable condition for unity is that all seek to have the Lord's will done in their mortal bodies. This focus produces the pleasantness of unity which glorifies God. Romans 15:5-6 (RSV), "May the God of steadfastness and encouragement grant you to live in such harmony with one another, in accord with Christ Jesus, that together you may with one voice glorify the God and Father of our Lord Jesus Christ.?"