Who are you?

Of his fulness have all we received, and grace upon grace.
This is my beloved Son, in whom I am well pleased. — Behold, what manner of love the Father hath bestowed upon us, that we should be called the sons of God.
His Son, whom he has appointed heir of all things. — If [we are] children, then heirs; heirs of God, and joint‑heirs with Christ; if indeed we suffer with him, that we may be also glorified together.
I and my Father are one. The Father is in me, and I in him. — My Father, and your Father; and ... my God, and your God. — I in them, and thou in me, that they may be made perfect in one..

It is astounding, but as a believer, a Christian, you participate in God's own nature.  Peter calls us "Partakers of the Divine Nature..." In Greek, the word "nature" is phusis, which paraphrased is, "What a thing is made of."  So Peter is saying, we are made of the same "stuff" as God once we believe.  How this can be is another mystery, but your connection with God that starts when you believe in Jesus Christ alters your very nature.  Yes, you are the same person, but no, you are not only the same person.  Once you believe, you partake of the Divine nature, a "sharer" in what God is.

The morning's verses confirm this: Yes, Jesus is "the Beloved Son;" but so are we the sons of God. Yes, Jesus is the Son, the Christ, the appointed heir of all things; but we are also joint-heirs with Him of all that God has given Him.

Yes, Jesus is one with the Father, and the Father is in Him and He is in the Father, and so are we one with and in Him.

In other words, God has brought us so much through His Son Jesus Christ that we are literally the branches of which He is the tree; we are parts of His body, His flesh, His bones. We are so united with Him once we believe that it is impossible to disconnect us from Him.  This is really the foundation of the doctrine of "eternal security;" it's not that we lose our sinfulness when we become believers, or even that we will not fall away for a time, or that we can't make terrible mistakes.  It is that we are "connected." This connection is just like the parts of a body, and He is determined to have every part of His body complete.