I think I've been able to put some of the details together.
Christ came out of God before all creation and shared God the Father's spirit. They were different from each other, but shared one spirit.They are one by sharing one spirit. We receive Christ's Spirit, which is also God the Father's Spirit so Christ is in us and God the Father is in Christ. I'm not sure yet how we are in Christ. (John 14:20 At that day ye shall know that I am in my Father, and ye in me, and I in you.)
We receive Christ (The Comforter, Spirit of Truth) by way of God's Holy Spirit. (John 14:23 Jesus answered and said unto him, If a man love me, he will keep my words: and my Father will love him, and we will come unto him, and make our abode with him.)
Romans 8:9 But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of his.
Does that sound right?
What happens to our spirit when we receive the Holy Spirit? If our spirit becomes one with the Holy Spirit that would explain how we are in Christ.