the Holy Spirit
The Holy Spirit is the divine Agentwho expresses to a believer the love of God, that is, God’s love for him. The reality of God’s love in a believer’s heart gives the assurance, even the guarantee, that the believer’s hope in God and His promise of glory is not misplaced and will not fail. This ministry of the Holy Spirit is related to His presence in believers as the seal of God (Eph. 4:30) and as the earnest or down payment of their inheritance in glory (2 Cor. 1:21-22; Eph. 1:13-14). Later Paul wrote that the Holy Spirit Himself has been poured out in believers (Titus 3:6). Each believer has the Spirit of Christ (Rom. 8:9) in the sense that He is indwelt by the Holy Spirit (cf. 1 John 3:24; 4:13).
Witmer, John A. “Romans.” The Bible Knowledge Commentary: An Exposition of the Scriptures. Ed. J. F. Walvoord & R. B. Zuck. Vol. 2. Wheaton, IL: Victor Books, 1985. 456. Print.