Colossians 2:9-10 (NLT)
9 For in Christ lives all the fullness of God in a human body. 10 So you also are complete through your union with Christ, who is the head over every ruler and authority.
Christ is in God and God is in Christ. The Holy Spirit that indwells within us is in Christ and therefore also in God. So we too are in God and Christ when we have received the Holy Spirit through faith in Jesus Christ.
In Christianity we refer to The Father, Jesus Christ the Son and the Holy Spirit as the Trinity or one God in three persons. The three persons are distinct, yet they are a single in nature. Each one has its purpose and works together in harmony.
"Catechism of the Catholic Church, 253-267: The dogma of the Holy Trinity says that the whole work of creation and grace is seen as a single operation common to all three divine persons, in which each shows forth what is proper to him in the Trinity, so that all things are "from the Father", "through the Son" and "in the Holy Spirit".
In Matthew 22:41-46 it is said, �Then, surrounded by the Pharisees, Jesus asked them a question: �What do you think about the Messiah? Whose son is he?� They replied, �He is the son of David.� Jesus responded, �Then why does David, speaking under the inspiration of the Spirit, call the Messiah �my Lord�? For David said, �The Lord said to my Lord, Sit in the place of honor at my right hand until I humble your enemies beneath your feet.� Since David called the Messiah �my Lord,� how can the Messiah be his son?� No one could answer him. And after that, no one dared to ask him any more questions.
From the beginning The Son and The Holy Spirit were with The Father. We see references in the Old Testament where people were filled with The Holy Spirit. David said in Psalm 51, �Do not banish me from your presence, and don�t take your Holy Spirit from me.� In Genesis God said, �Let us make human beings in our image, to be like us.� When man ate from the tree of knowledge of good and evil, God said, �Look, the human beings have become like us, knowing both good and evil.�
An analogy I like to use is that of an egg. If we hold up an egg we easily identify it. Yet an egg is made from three distinct parts, the shell, the yoke, and the white. Yet all parts work together to form a new born chicken. All parts of the Trinity work to form a new born man. For in receiving Christ man receives the Holy Spirit and is in communication with The Son who speaks to The Father on our behalf. We are redeemed and made new and are bonded to Christ who makes us adopted heirs to eternal life.
In John 14:9-11, �Jesus replied, �Have I been with you all this time, Philip, and yet you still don�t know who I am? Anyone who has seen me has seen the Father! So why are you asking me to show him to you? Don�t you believe that I am in the Father and the Father is in me? The words I speak are not my own, but my Father who lives in me does his work through me. Just believe that I am in the Father and the Father is in me. Or at least believe because of the work you have seen me do.�