God’s organic salvation is carried out by the two divine transfers, out of Adam into Christ and out of the flesh into the Spirit, in one spiritual union. This is for us to reign in life with grace over all things unto eternal life. All the things mentioned in Romans 5 through 16 are under the reigning in life, and the totality, the aggregate, of the eternal life is the New Jerusalem. The New Jerusalem is the divine and human constitution, which is just Christ as the Son of Man. Since the Son has been incorporated with us, we and the Son become the incorporation, the uplifted standing stairway, the ladder that joins earth to heaven and brings heaven to earth.
The one spiritual, practical, and experiential union is of the Spirit with our spirit, the regenerated spirit of the believers in Christ indwelt by the Spirit (Rom. 8:16a, 11b). The two spirits are united together to be in one union. It is not only that the Spirit witnesses and our spirit witnesses also. Rather, it is that the Spirit witnesses with our spirit. This indicates that our spirit must take the initiative to witness first; then the Spirit will witness with our spirit. This reveals that the Spirit of God today, the all-inclusive Spirit of the Triune God, dwells in our regenerated human spirit and works in our spirit. These two spirits are one; they live together, work together, and exist together as one mingled spirit.
The Spirit witnesses with our spirit that we are the children of God and the heirs of God. This means that we will inherit God. We are the joint heirs with Christ and possess the spirit of sonship to cry, "Abba, Father" (vv. 16-17a, 15). Abba is an Aramaic word that means "father," and Father is the translation of the Greek word Pater. Such a term was used first by the Lord Jesus in Gethsemane while He was praying to the Father (Mark 14:36). The combining of the Aramaic title with the Greek title expresses a stronger affection in crying to the Father. Such an affectionate cry implies an intimate relationship in life between a genuine son and a begetting father. After being regenerated, we are no longer merely God’s creatures; we are His children. Because we have now been born of God and are related to Him in life, it is very normal and sweet for us to call Him Father. When we cry, "Abba, Father," there is the witnessing of the Spirit. Such a witnessing testifies to us and assures us that we are the children of God, who possess His life; it also limits us and restricts us to a living and walk that are according to this life, in keeping with our being children of God. The Spirit witnesses to our most basic and elementary relationship with God, namely, that we are His children. Therefore, this witnessing of the Spirit begins from the time of our spiritual birth, our regeneration.
The Spirit of life and our regenerated spirit become one in one spiritual union. We then pray with groanings by the interceding Spirit (Rom. 8:26). We do not know how to pray as we ought, but the Spirit is with us in like manner and helps us in our weakness. The weakness here is our ignorance of how we should pray. We do not know the kind of prayer God desires, and we are not clear how to pray, according to the burden we feel, for our being conformed to the image of God’s Son; hence, we groan (v. 23). In our groaning the Spirit groans also, interceding for us. His interceding is mainly that we may experience the transformation in life for growth into the maturity of sonship that we may be fully conformed to the image of God’s Son (v. 29).
(Crystallization-Study of the Complete Salvation of God in Romans, Chapter 3, by Witness Lee)