The short answer
HaShem's own breath and presence, ruach meaning wind, breath, and spirit at once. Not a separate person pictured as a second "He," but HaShem's own life moving in and on His people.
The full answer
Ruach is a rich Hebrew word that means wind, breath, and spirit all at once; Hebrew does not make you choose. The Ruach HaKodesh, usually translated the Holy Spirit, is God's own breath and living presence, the same breath that gave Adam life and that writes God's instruction onto the human heart.
Here is the part to get right: the Ruach is not a separate person standing beside God, a second He. It is God's own life and presence at work in and on His people. So when Scripture shows the Spirit acting, the action is God's. He moves, He fills, He writes, by His own breath.
Passages this rests on
- Genesis 1:2
- Genesis 2:7
- Job 33:4
- Ezekiel 36:26-27
- Ezekiel 37:9-10
- Jeremiah 31:33
- Psalm 51:11
- Psalm 104:30
- Isaiah 63:10-11