The "inner man," "inner self," or "inner being" in passages such as Romans 7:22, 2 Corinthians 4:16, and Ephesians 3:16, and common parlance, is a reference to the spiritual or personal aspect of a person. We think of the "outer man" as our body or outward appearance or behavior, whereas the inner man is associated with things like our mind, heart, soul, and spirit.
What is the inner man?
Our bodies are the physical vessels through which we experience life. Our inner person is often expressed through our bodies, and the things we experience through our physical senses impact our inner man. Those who believe in Jesus Christ have the indwelling Holy Spirit, for whom our bodies function as a temple (1 Corinthians 6:19–20). Christians are called to offer our bodies to God as living sacrifices (Romans 12:1–2). However, it is largely in the inner man that we commune with God and from which we relate with others. It is in our inner person that we experience things like love, peace, hope, and joy.
Though we might be able to hide our inner person from the world, we cannot hide it from God. He knows all and sees all, even into our hearts (1 Samuel 16:7). This is a comfort to us because we know God sees and cares about our deepest hurts. He knows our personality quirks, our deepest longings, our greatest joys, our musings, our fears, and the like. If we are in Jesus Christ, then God is our Father and we know He views us with kindness and compassion. We can trust Him with the secret things of our inner person.
We also know that God sees the sin that is so often present in our inner man. The Bible clearly states that God is not only concerned with the person we show to the world (our behavior), but that His judgment extends even to the hidden motives of our hearts (Romans 2:16). This is demonstrated in Jesus' rebuke of the leading Jewish religious people of His day, the Pharisees. The Pharisees had an external or outward righteousness. They followed the law of God to the letter. They tithed even down to their spices (Matthew 23:23–24). However, inwardly they were proud, self-righteous, and spiritually dead (Matthew 23:27–28). Jesus' standard of righteousness extended beyond outward conformity to God's law to the inner attitudes of the heart (Matthew 5:21–48). God commands holiness and perfection not only in our outward acts and performance; He demands holy and pure motives from our inner persons, our hearts (1 Peter 1:16).
This creates a bit of a conundrum since no one, not one of us, is holy as God is holy (Romans 3:10–11). None of us have perfectly pure motives to please God in all we think, feel, and do. Our hearts are sinful by nature and by practice. We need spiritual heart transplants. Thankfully, this is exactly what God had in mind and exactly what He does for His children (Ezekiel 11:19–20). The theological term for this spiritual heart transplant is regeneration. It is pictured also in Nicodemus' interaction with Jesus Christ. Jesus told Nicodemus that he must be born again (John 3). This assumes the spiritual deadness of mankind and the need for a new spiritual nature and heart (Ephesians 2:1–10). Men and women need nothing short of a spiritual birth (John 3:3), and this is what the Spirit of God provides through Jesus Christ (John 3:7–8).
When we receive God's forgiveness, which is offered to everyone who will believe through putting faith in the life and death of Jesus Christ and receiving Him as our Lord and Savior (John 3:16–18), the Holy Spirit comes to live within us giving us a new heart and new nature (Ephesians 1:13–14). We become children of God (John 1:12) and are declared to be righteous in a judicial sense (this is referred to as "justification"). However, we still retain the sinful tendencies of our inner man. The actual process of transformation (referred to as "sanctification") is progressive. It is in our inner person that God's transforming work of sanctification occurs (Philippians 2:12–13).
The Spirit of God is responsible for Christians being referred to as new creations (2 Corinthians 5:17). These new natures do battle against our old sinful natures or "old man" (or "flesh") that remains in us (Galatians 5:17–24; Ephesians 4:17–32). This new inner nature desires to live for and please God not only through outward behavior but by keeping in step with the Spirit in all ways. The Holy Spirit within us gives us the will and strength to resist sin and grow in righteousness. He inclines our hearts toward the things of God and helps us better understand God's love and grow in obedience to God. The ultimate goal of our new natures is to be conformed completely to the image of Jesus Christ (Romans 8:29). One day, when we are with Christ, our inner man will be completely transformed. Sin will no longer be an issue and we will experience unhindered fellowship with Him.
What is the human soul, according to the Bible?
What is the difference between the soul and the spirit?
What is the heart, according to the Bible?
Do we have a body, soul, and spirit? Are we made of two parts or three? Dichotomy or trichotomy?
What is human nature?
Truth about Humanity