I think Romans 8 is one of the best post-gospel accounts on the activity and role of the Holy Spirit. These statements are meant to be understood very plainly.
- The Spirit directs, governs our minds. (v 6)
"the mind governed by the Spirit is life and peace. "
- We are obligated (though not forced) to be led by the Spirit. (v 12, 13, 15)
"we have an obligation... to live according to the Spirit."
"The Spirit you received does not make you slaves"
- Those who are led by the Spirit are considered God's children. (v 14)
"For those who are led by the Spirit of God are the children of God."
- The Spirit testifies with our spirit that we are God’s children (v 16) and about many other things - cross reference previous statements both here and in John 14, 15, 16, 17.
"The Spirit himself testifies with our spirit that we are God’s children"
The Spirit is not a euphemism for something else - like a biblical set of rules. He is a separate spiritual entity that was there in the very beginning.
In the beginning God created the heavens and the earth. Now the earth was formless and empty, darkness was over the surface of the deep, and the Spirit of God was hovering over the waters.
And He interacts with our spirit.