“As the oil ran down Aaron’s head to his body (cf. Psalm 133:1-2; Lev. 8:12), so the Spirit would run down from Christ over our Head to His Body, the church. Thus we become ‘partakers of His anointing’ (Heidelberg Catechism, #32).
The Spirit, through whom the Father had eternally loved His Son, would now anoint believers ‘that they may be one as we are one’ (John 17:22). One with the Lord, one with each other.
This is salvation with jam on top. In fact, the more Trinitarian the salvation, the sweeter it is.
For it is not just that we are brought before the Father in the Son; we receive the Spirit with which He was anointed. Jesus said in John 16:14 that the Spirit ‘will bring glory to Me by taking from what is mine and making it known to you.’
The Spirit takes what is the Son’s and makes it ours. When the Spirit rested upon the Son at His baptism, Jesus heard the Father declare from heaven: ‘You are My Son, whom I love; with You I am well pleased.’
But not that same Spirit of sonship rests on me, the same words apply to me: in Christ my high priest I am an adopted, beloved, Spirit-anointed son. As Jesus says to the Father in John 17:23, You ‘have loved them even as You have loved Me.’
And so, as the Son brings me before His Father, with their Spirit in me I can boldly cry, ‘Abba,’ for their fellowship I now freely share: the Most High my Father, the Son my great brother, the Spirit no longer Jesus’ Comforter alone, but mine.”
–Michael Reeves, Delighting In The Trinity: An Introduction to the Christian Faith (Downers Grove, IL: InterVarsity Press, 2012), 74-75.