"Unless you are converted..." said Jesus Christ in Matthew 18:3, "you will by no means enter the kingdom of heaven." Clear words, those. And vital ones, too. This plain and simple statement should rivet our attention. It literally demands that we find out what Jesus Christ meant — what it means to be converted! For unless we know what true conversion is, and further, unless we become converted, we will have no place in the Kingdom of God, and our hope is lost. This is what Christ our Savior said.
The basic doctrine
Conversion is the changing of our minds and actions from the carnal way of the natural man to the spiritual way of thinking and acting of God Himself. It includes changing, or converting, us from the physicochemical state of mere existence in which we now find ourselves to the immortal, glorified life that God Himself enjoys. It begins at baptism with the receipt of the Holy Spirit, continues throughout life with the spiritual growth of the individual and culminates at the resurrection when one is born into God's Kingdom as a new creature — a spirit-composed member of God's Family.
The usual teachings of this world
The religious teachers of this world have not fully understood this vital process. They have instead attached a meaning to the word conversion far diluted from the pure truth of the Bible. Commonly the term is used to mean the simple change one makes when he embraces a new faith or denomination. Hence one who changes his beliefs, as it were, from, say, Judaism to Christianity (of whatever denomination) is said to "convert." But this is not the true substance and meaning of conversion as explained in God's holy Word. To the contrary, Christ's statement cited above (that unless they were converted they would not enter the Kingdom of God) was made to ones already labeled by the Bible as "disciples." Certainly such ones would already be professing a belief in Jesus and hence be already "converted" in the sense most often meant by this world. Further, Christ told Peter yes, the apostle Peter — "When thou art converted, strengthen thy brethren" (Luke 22:32, Authorized Version). Clearly, even the apostles, although in every way expressing their profound belief in Jesus, were not, during Jesus' life, even themselves yet converted. Just what, then, is true conversion? To begin, we need look no further than the plain and simple meaning of the word conversion itself as we might use it in any other, nonreligious context.
The Bible teaching
To convert something means to change it from one purpose or form or use to another one. This is not hard to understand when applied to the physical world and context, such as in the case of the conversion of a farm into a real estate subdivision for homes. The use and purpose of the land has been changed from one thing into something different. Likewise, when one is converted, or goes through conversion, he or she is changed from one thing — one type of creature — into another totally different type of person. This conversion is not merely a change in profession of faith (although that is included), or of some merely outward form, but is a total and inward change. Of course, to change a person means to change his or her mind — that is, the way one thinks — for a person is his or her mind. Proverbs 23:7 says, "As he thinks... so is he." One's mind is the core of one's personality, character and thought. To change a person you do not simply change the hairstyle or wardrobe. To change the person you change his or her mind (Romans 12:2). The key to understanding conversion is to understand that there are two possible types of minds that a person can possess (with God's help, in the case of one of them). There is the carnal mind, and there is the spiritual mind. The carnal or fleshly mind (the word carnal literally means "fleshly") is the natural mind that a person has apart from God and influenced by this world. It is not the mind of a mere animal, but the superior mind of a human, and consists of the brain and the spirit in man (this spirit in man should not be confused with the pagan concept of the "immortal soul"). Paul wrote of this carnal mind when he asked, "What man knows the things of a man except [by] the spirit of the man which is in him?" (I Corinthians 2:11). But this mind, although it is the mind that occurs naturally and normally within a man, is insufficient for salvation. Paul goes on to explain, in part, why: "The natural man does not receive the things of the Spirit of God, for they are foolishness to him; nor can he know them, because they are spiritually discerned" (I Corinthians 2:14). So one reason why the carnal mind is not sufficient is that it cannot discern spiritual things, and indeed such spiritual things seem like foolishness to it. But Paul in another place proclaims the need to convert the carnal mind to the spiritual mind in even stronger terms: "To be carnally minded is death, but to be spiritually minded is life and peace. Because the carnal mind is enmity against God; for it is not subject to the law of God, nor indeed can be. So then, those who are in the flesh [those who have a carnal mind] cannot please God" (Romans 8:6-8). This, then, is the reason Christ said if we are not converted we cannot enter the Kingdom of God. The carnal, unconverted mind cannot know the things of God, cannot obey God, cannot please God. It is therefore cut off from God. "To be carnally minded is death" (verse 6)! But the spiritual mind, on the other hand, is different from the carnal mind. It has an additional component — the Holy Spirit of God. Indeed, this is what Paul says next: "But you are not in the flesh [you do not have a mere carnal mind] but in the Spirit [you have a spiritual mind] if indeed the Spirit of God dwells in you. Now if anyone does not have the Spirit of Christ, he is not His" (verse 9). Yes, to have a spiritual mind and be converted — to even be a Christian in God's eyes — you must have a spiritual mind. And that only comes from having God's Spirit dwelling within you (I Corinthians 2:11-12). Acts 2:38 tells us how we may receive that converting Holy Spirit of God. Upon repentance, we can be baptized, and after the laying on of hands, which follows baptism, we will receive the gift of the Holy Spirit — the Holy Spirit that gives us a spiritual mind and converts us to creatures God can use. Therefore, to become converted, we must repent and be baptized. There is no other way. But even here, some have misunderstood. They think that once a person has received God's Spirit, conversion is total and complete, and that the person cannot or will not sin at all — ever. Such is not the case. Conversion is a process, and is likened in the Bible to the process of a baby's gestation and birth. In both cases, the newly conceived person — be it a physical child or a spiritual child of God — must grow and develop over time before birth. Spiritually, Paul talks about this growth process in many places, including Romans 7. Read all of Romans 7 and see how Paul describes the struggle he had to endure while the still remaining carnal component of his nature struggled against the Spirit of God dwelling within him. In the case of a physical child, in time it will be born as a separate person able to live on its own. Likewise, a spiritual convert must change and grow until the resurrection, when he or she will be literally "born again" (John 3:3-6) — this time of the Spirit — and will enter God's Family as a spirit being. At that time the conversion from physical to spiritual will be complete, and our carnal, fleshly mortality will be displaced and "swallowed up by life" (II Corinthians 5:4). We will be quite literally a new creature! Truly, to see the Kingdom of God, we must indeed be converted — in mind and, eventually, in body as well.
The process of conversion is so important that it is helpful to remember, and perhaps mark in one's Bible, key verses describing this process. Here are some of them: Matthew 18:3 — we must be converted or we will not enter God's Kingdom. Luke 22:32 — conversion is not merely belief, because even Peter, though he believed, was told he had yet to be converted. Romans 12:2 — conversion involves a change in our mind. I Corinthians 2:9-14 — the carnal mind does not understand spiritual things — only the spiritual mind does. Romans 8:5-9 — the carnal mind is not sufficient for salvation, and the indwelling of God's Spirit is the source of the spiritual mind. Acts 2:38 — the Spirit of God is given to those who repent and are properly baptized. "Unless you are converted..." proclaimed Jesus, "you will by no means enter the kingdom of heaven." But with proper baptism and the consequent receipt of God's Holy Spirit, we can become a new creature (II Corinthians 5:17) — converted — with the hope of eternal glory!