Exodus 29:2 NKJV
and unleavened bread, unleavened cakes mixed with oil, and unleavened wafers anointed with oil (you shall make them of wheat flour).
When the priests were consecrated, oil was poured on their heads. They also ate unleavened bread and wafers mixed with oil.
Spiritual parallel: A symbol of the anointing and the Holy Spirit was poured on their bodies. They also took the symbol of the anointing and the Holy Spirit inside their bodies. The oil upon would represent the equipping for ministry to others. The oil within would represent their connection to the Spirit of God for their personal lives. The anointing within would also help with ministry.
1 John 2:27 NKJV
“But the anointing which you have received from Him abides in you, and you do not need that anyone teach you; but as the same anointing teaches you concerning all things, and is true, and is not a lie, and just as it has taught you, you will abide in Him.”
John 14:16-17, 26 NKJV
And I will pray the Father, and He will give you another Helper, that He may abide with you forever— the Spirit of truth, whom the world cannot receive, because it neither sees Him nor knows Him; but you know Him, for He dwells with you and will be in you.
But the Helper, the Holy Spirit, whom the Father will send in My name, He will teach you all things, and bring to your remembrance all things that I said to you.
This will help explain why we sometimes feel the anointing coming upon us to minister. Yet we have that anointing inside of us to give us access to the ministry of the Holy Spirit for ourselves as well as for ministry.