Very, very interesting. Apparently it is a technical state or condition that exists when a person is having a spiritual connection via some sort of a transe.
For someone who isn't born again, this is impossible to really truly grasp. Paul meant literally what he said. There is no need to invoke Philo of Alexander (the father of spiritualizing everything) who was an unsaved jewish philosopher. He could know nothing about the new birth and the new spirit.
This is what all the business with circumcision pictured. In the new birth event, the old spirit is cut away in the dividing of soul and spirit and a new spirt, one made alive and quickened from God is installed.
It exists right along side the sinful body. This is a never-before-seen creation in the universe.
Gal 2:20I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me.
Therefore if any man be in Christ, he is a new creation: - 2 Cor. 5: 17
But this shall be the covenant that I will make with the house of Israel; After those days, says the LORD, I will put my law in their inward parts, and write it in their hearts; and will be their God, and they shall be my people. Jer. 31:33
The installation of a new spirit that is truly alive and incapable of perishing is simply the fulfillment of God's previous promises.... originally intended for Israel, but they didn't want it. Paul was surprised and didn't really know what to make of praying in tongues because while it really was his spirit praying....his fleshly mind didn't comprehend the meanings. So, he just decided that while that was going on, he'd just go ahead and pray with his fleshly mind as well.
1 Cor. 14:14 For if I pray in an unknown tongue, my spirit prayeth, but my understanding is unfruitful. 15 What is it then? I will pray with the spirit, and I will pray with the understanding also:
Millions of people have experienced this exact same phenomenon after they invited Jesus into their heart (spirit). I know lots of folks who have.
Apparently, the new spirit is also capable of being in a different place than the body and yet, both are actually "you".
This is all a very far cry from the heralds of Brooklyn, and yet it is right there in the New Testament bible plain as day.