Ephesians 4:21-24 "if indeed you have heard Him and have been taught in Him, just as truth is in Jesus, 22 that, in reference to your former manner of life, you lay aside the old self, which is being corrupted in accordance with the lusts of deceit, 23 and that you be renewed in the spirit of your mind, 24 and put on the new self, which in the likeness of God has been created in righteousness and holiness of the truth."
What is man?
Who are you? Whose are you? These are two questions that are fundamental to grasping one's identity. How people answer these two questions will determine how they understand themselves and for whom they live their lives. God's main aim in Christian growth is to transform a person from the inside to the outside to Christ-likeness.
Understanding "who you are" and "whose you are" entails answering a third related question: "what are you?" Secularists will tell us that people are nothing more than the sum-total of the electrical impulses traveling between the neurons in the brain. In short - man is only a physical, biological machine that has a consciousness emerging out of the sum of the parts. Man lives, dies, and no more.
The Bible itself asks this question "what is man?" in Psalm 8:3-4 "What is man that You take thought of him, And the son of man that You care for him?" The key to understanding how to answer the question "what is man?" is implied in King David's question itself: "You take thought of Him". Scripture uniformly states that mankind cannot understand "what they are" nor "who they are" without identifying themselves in relationship with God.
Man's true humanity cannot be properly understood apart from Jesus Christ
The goal of salvation is reconciliation with God through faith in Jesus Christ. The marvel of the Gospel is that Jesus Christ, the Eternal Son, came to this earth and took upon himself the nature of those whom needed to be reconciled and transformed. As fully God - Jesus Christ perfectly reveals to us the God with whom we need reconciled and the God Who desires to be reconciled to us. 2 Corinthians 5:18-19 states: "Now all these things are from God, who reconciled us to Himself through Christ and gave us the ministry of reconciliation, 19 namely, that God was in Christ reconciling the world to Himself, not counting their trespasses against them, and He has committed to us the word of reconciliation."
Simultaneously as God, the Eternal Son is now also man. Therefore in answering the question: "what is man?", the only accurate answer to be given is by looking at the humanity of Jesus Himself. The writer of Hebrews takes the question of Psalm 8:3-4 and casts it in light of Jesus Christ's incarnation in human flesh in Hebrews 2:9 "But we do see Him who was made for a little while lower than the angels, namely, Jesus, because of the suffering of death crowned with glory and honor, so that by the grace of God He might taste death for everyone."