The Holy Spirit through the Apostle Peter describes the man’s spirit as “the inward man of the heart.” (1 Peter 3:4). It is the inward man who gives this outer man his appearance. Spiritual things are revealed to the "hidden man of the heart" not the mind, the intellect. The Holy Spirit makes His home in the "hidden man." It is very important that we understand that it is our recreated spirit that understands spiritual things, whereas it is our conscience that is the voice speaking to our reasoning faculties. So when we read the words, in Him, in Whom, in Christ, it is God’s Word for us now.
Jesus said, "I am the vine, you are the branches. He who abides in Me, and I in him, bears much fruit; for without Me you can do nothing." (John 15:5) The branch is a part of the vine as the vine is a part of the branch. The two are one. This becomes a reality in us the moment we confess Christ as Lord and take Him as our Savior. We immediately receive eternal life, the Nature of the Father which makes us new creations. The Holy Spirit through the Apostle Paul tells us, "So that if anyone is in Christ, he is a new creature: the old state of things has passed away; a new state of things has come into existence. And all this is from God, who has reconciled us to Himself through Christ."
(2 Corinthians 5:17-18 Weymouth) and "This we recognize, that our former self was nailed to His cross with Him, so that that body which was the instrument of sin might be made impotent for evil, so that we could not any longer be slaves of sin." (Romans 6:6 Ways Version)
Notice carefully that the part of us that was recreated, made new, was our spirit, which Peter calls "the hidden man of the heart" and Paul calls "the old man." This old man was nailed to the cross with Christ. It was not our physical body, not our soul, that is, the mind, will, emotions and intellect, our reasoning faculties, but our spirit. "Do not lie to one another, since you have put off the old man with his deeds, and have put on the new man who is renewed in knowledge according to the image of Him who created him." (Colossians 3:9-10) When Christ was raised from the dead a "new man" was raised with Him. That new self is the recreated human spirit, the hidden man of the heart. Now the physical body, which is the home of the five senses, and the soul, must be brought into conformity with Christ, who is the Head of the Body. As it was with Adam, before the fall, the body and soul must become subject to our recreated spirit.
The Apostle Paul says it this way, "I beseech you therefore, brethren, by the mercies of God, that you present your bodies a living sacrifice, holy, acceptable to God, which is your reasonable service. And do not be conformed to this world, but be transformed by the renewing of your mind, that you may prove what is that good and acceptable and perfect will of God." (Romans 12:1-2) Let’s be honest, there is not much on going teaching on the subject in regard to devoting our bodies to God’s service and the necessity of a renewed mind. We need to understand that all the knowledge acquired prior to being born again comes from the five senses which are a part of the physical body and can never be renewed. They can be brought into subjection; they can be controlled, but they cannot be renewed. Our spirit is recreated, but the mind, our brain, receives its knowledge from the five senses, and can be brought into subjection to God’s Word. The mind slowly but surely as it feeds on the Word, meditates in the Word, practices and lives the Word, will eventually come into align with the recreated spirit.
Here in Romans 12:1-2 Paul is addressing what the believer must do concerning the two parts of our being, body and soul, that were not recreated when we became born again. The first thing is to bring our body, the five senses into subjection to the recreated human spirit. Next, renew our mind which is accomplished through the Word of God. Although a person becomes born again, he/she still possess the same mind and body that had been under the dominion of the devil. The Holy Spirit through the Apostle John tells us, "In this the children of God and the children of the devil are manifest: Whoever does not practice righteousness is not of God, nor is he who does not love his brother." (1 John 3:10) There are only two families on earth and every person is part of one or the other. If one is not born again, they are a child and under the dominion of the devil.
This is the reason that it is so important for believers to daily present their bodies to God and to continuously renew the mind and bring them into harmony and subjection with the recreated spirit, the new self. This is also the reason why many believers struggle with “the weights and sin that so easily ensnare.” They do not know who they are in Christ, who Christ is in them and how the Father sees them, Why? Their minds are not being or have never been renewed. The writer of Hebrews tells us, "For the Logos of God is a living thing, active and more cutting than any sword with double edge, penetrating to the very division of soul and spirit, joints and marrow, scrutinizing the very thoughts and conceptions of the heart." (Hebrews 4:12 Moffatt)
It may be difficult for your mind to assimilate this, that is, to allow the Word to utterly dominate, but that must come or else believers are going to live in a sort of semi-spiritual darkness. But the more the mind is renewed, the better we will come to know the will of the Father and eventually we will not be satisfied with good and the acceptable will of God, but only want the perfect and the well-pleasing will of the Father. To God be all the glory, Amen...