On Mount Sinai Moses asked God to tell Him who He is, His name. God said He is I am that I am. God is existence. Jesus reveals God is Three Divine Persons, the Father, Son and Holy Ghost. This is who God is. We are baptized in the name of the Trinity.
There is a difference between who God is and what God is.
God is good. God is love. God is life, God is truth. God is just. God is infinite. God is omniscient. God is omnipotent. These are the infinite divine perfections, what God is. The three divine persons share the same nature.
The three persons lack nothing of what the other is. If one possessed something another lacked one would not be infinite.
All humans share human nature. We are not the same. We have unique personalities, physical characteristics, etc. In our human nature we do what we do, speak, sing, see, walk, laugh, cry, breathe, eat, drink, pray, sin. If I lacked sight I would still be human.
We can not do what a fish does, lacking fish nature.
We can do what God does. We can love, be truthful, create new life, be just, have knowledge, be merciful, etc. We are spiritual and material beings.
We can be what God is, but not who God is.
God allows us and empowers us by grace to do what He does. He shares His nature with us. In heaven you will see God who is light. On earth we see reflections of light. In heaven we will see Him face to face.
Jesus who is who God is took on human nature. He became incarnate. He took His human nature with Him when He left earth. He sits at the right hand of the Father incarnate. He is God-man, sharing our nature.
God participates in human nature so that we can participate in divine nature. He lowered Himself and raises us. This does not make us who God is. It makes us what God is.
In the person of Jesus human nature and divine nature are joined, married. God marries His creation. The two become one.
We already do participate in divine nature when we love. We participate fully in heaven.
Life here is a foretaste, or it can be so if we choose.
The father knows and loves the Son. He gives Himself to the Son entirely. Jesus says everything the Father has is mine. The Son gives Himself back to the Father. Love gives love to love. God is trinitarian.
We are made to participate in the life of the Holy Trinity.
We learn from the beginning we are made in the image and likeness of God. The temptation was to become like God. Eve already was like God, made in His image.
So are we.
The difference between God and us is we are made. Jesus is not made. He is eternally begotten of the Father.
When a woman marries a man she takes his name, at least until this confused age. The Church is the bride of Christ. The two become one. We are called by His name, Christian.
A fish can not marry a tree. In order to marry, become one with, two beings must share the same nature. God marries us.