Spirit of holiness = Holy Spirit?
English Revised Version, Ro 1:
>1 Paul, a servant of Jesus Christ, called to be an apostle, separated unto the gospel of God, 2 which he promised afore by his prophets in the holy scriptures, 3 concerning his Son, who was born of the seed of David according to the flesh, 4 who was declared to be the Son of God with power, according to the spirit of holiness, by the resurrection of the dead.
Surprisingly, the term appeared only once in the Bible.
Many interpreters (e.g., Cyril of Jerusalem) understood "Spirit of holiness" as another term for the Holy Spirit. However, let's look at the parallelism:
descended from David according to the flesh
Son of God in power according to the Spirit of holiness
Son of David || Son of God.
Flesh || Spirit of holiness.
Horizontally, Jesus was the Son of David according to the flesh, in a bodily sense.
Vertically, Jesus was the Son of God according to the sense of the Spirit of holiness.
Horizontally, Paul was talking about Jesus.
Vertically, I believe Paul was also talking about Jesus, not the Holy Spirit.
The Spirit of holiness was Jesus' human spirit. It referred not to another person (the Holy Spirit) but to Christ's own spiritual being, characterized by perfect holiness.
Paul contrasted the horizontal and vertical aspects of the one person, Jesus Christ. The rest of the passage bore this out:
>even Jesus Christ our Lord, 5 through whom we received grace and apostleship, unto obedience of faith among all the nations, for his name's sake: 6 among whom are ye also, called to be Jesus Christ's.
In this paragraph, Paul stressed the singular person of Jesus. The immediate context was thoroughly Christological.
Spirit of holiness = Holy Spirit?
I don't think so. Paul was talking about Christ’s own human spirit, or his spiritual nature, rather than the Third Person of the Trinity.