In Romans 8:2 Paul refers to the Spirit as the Spirit of life. Paul does not refer simply to the Spirit but to the Spirit of life. In so doing, he stresses the matter of life. In the second half of verse 6 Paul continues this emphasis when he says, “The mind set on the spirit is life and peace.” Verse 9 then reveals two additional titles of the Spirit. This verse reads, “You are not in the flesh, but in the spirit, if indeed the Spirit of God dwells in you. Yet if anyone does not have the Spirit of Christ, he is not of Him.” In this verse Paul calls the Spirit the Spirit of God and the Spirit of Christ. Thus, in Romans 8 Paul uses three different titles when speaking of the Spirit—the Spirit of life, the Spirit of God, and the Spirit of Christ. This reveals that the Spirit of God is the Spirit of Christ and that the Spirit of Christ is the Spirit of life. God is in Christ (John 14:10-11). God is the Father, Christ is the Son, and the Father and the Son are one (10:30). Not only is God in Christ, but this Christ is also life (11:25; 14:6). God is in Christ to be life to us (Col. 3:4). Moreover, God in Christ is life to us as the Spirit. This is why Paul uses these three titles in Romans 8 to speak of the Spirit. God is in Christ to be life to us as the Spirit of God, the Spirit of Christ, and the Spirit of life.
How are we able to have a share in this Spirit? Romans 8:14 tells us the answer: “For as many as are led by the Spirit of God, these are sons of God.” This indicates that we have a share in the Spirit by means of our regeneration, our rebirth, which has made us sons of God. Because we have been regenerated to be the sons of God, we have a share in the Spirit of God. Verse 15 continues, “You have not received a spirit of slavery bringing you into fear again, but you have received a spirit of sonship in which we cry, Abba, Father!” The reason we cry “Abba, Father” is that we have received a spirit of sonship. This corresponds with Galatians 4:6, which says, “Because you are sons, God has sent forth the Spirit of His Son into our hearts, crying, Abba, Father!” This verse begins with, “Because you are sons...” We were made sons by regeneration. God regenerated us with His Spirit (John 3:6), and we thus became sons of God. Because we are sons, God has sent forth the Spirit of His Son into our hearts, and we cry out to God as our Father.
Galatians 4:6 reveals a fourth title of the Spirit—the Spirit of God’s Son. The Spirit is the Spirit of God, the Spirit of Christ, the Spirit of life, and the Spirit of God’s Son. The Spirit of God’s Son corresponds to the spirit of sonship in Romans 8:15. God is in Christ, Christ is life to us, and this causes us to become sons of God. A son always has the life of his father. If you do not have your father’s life, you are not your father’s son. The relationship between a son and a father is one of life. In like manner, we are the sons of God because we have received the life of God through regeneration. Through whom did we receive the life of God? We received the life of God through the Spirit of God as the Spirit of the Son, who is the Spirit of life. It is the Spirit who brought the life of God into us. The Spirit is the reality of the life of God (John 16:13). In fact, He Himself is the life of God (11:25). This is why He is referred to as the Spirit of life. Without the Spirit, there is no life. The divine life of God is in the Spirit, and the Spirit is the very essence and element of the divine life. Thus, if you have the Spirit, you have the divine life, and if you have the divine life, you are a son of God.
How do we know that we have the Spirit of God within us? Romans 8:16 tells us the answer: “The Spirit Himself witnesses with our spirit that we are children of God.” We know that we have the Spirit within us because the Spirit witnesses with our spirit that we are children of God. Whenever we have the feeling that we are children of God, we must realize that this feeling is something of the Spirit. It may be very weak, but this little feeling is strong proof that we are indeed children of God and that we have the Spirit of God within us. Although we may be sinful, worldly, and weak, and although we may fall and commit sins against God, we still have the feeling within that we are children of God, and we still automatically and spontaneously call out to God, saying, “O Father, my heavenly Father.” This is proof that we have the Spirit of the Son witnessing in our spirit, which is the innermost and deepest part of our being. Even after we sin against God, we still sense in the innermost and deepest part of our being that we are children of God. We may feel sorrowful and ashamed of what we have done, yet we still sense in our deepest part that we are children of God. This proves that we have the spirit of sonship, which is the Spirit of God’s Son, the Spirit of life, the Spirit of Christ, and the Spirit of God.