When the holy spirit enters us does our spirit and his spirit become one spirit? Is there any scripture to back up this point?
The Holy Spirit and our spirit can NEVER become one. The Holy Spirit is one part of the Trinity. Our spirit is of sinners. God is holy and righteous. Only through our faith in Jesus Christ that God see us as righteous through Christ.
I believe that we are sinners and we are not righteous until we have faith in Christ. We are always sinners because this is what we are but through Christ, what He has done at the Cross that God can see us as the righteous through Christ. If He can make us righteous through Christ as you said, are you saying that you are in no sin right now?
Paul lets us know that even when we sin, it is no longer us who sin but the sin nature within us. Romans 7:20 We are now dead to sin. See Romans 7. Once we truly understand these things, we truly understand the "so great salvation" that was bought for us by the work of Jesus on the cross. Hallelujah
Absolutely. Galatians 2:19,20 are also wonderful verse to remember.
For I through the law died to the law that I might live to God.
20. I have been crucified with Christ; it is no longer I who live, but Christ lives in me; and the life which I now live in the flesh I live by faith in the Son of God, who loved me and gave Himself for me.