In addition to obedience to the Word and holiness of life (see Part One), the next mark of spiritual maturity is intimate fellowship with the Father.
3. Intimate Fellowship (8:15b)
God is no longer our angry judge. Before salvation, we were God’s enemies (8:7). But God justified us and declared us not guilty. God is no longer our angry judge but because of adoption God is our loving heavenly Father to whom we can go with child like dependence and cry, “Abba, Father.” “Abba” was Aramaic or Paul’s language as a child. It was the name he spoke when he was a child first called out to his earthly father. Now it was the name Paul used to call out to God in dependence and intimacy.
I can still remember with fondness when our boys were small, and I would come home after being gone for several hours. They would run through the house to meet me at the door, shouting “Daddy” and throw their arms around me. I now wish I had recorded that scene.
John wrote much about believers being the children of God as in 1 John 3:1. There is a mature fear (the OT is filled admonitions to fear God) and there is also an immature fear which John addresses in 4:18, “There is no (immature) fear in love; but perfect or mature love casts out (immature) fear: because (immature) fear has torment. He that fears is not perfect or mature in love.”
When I was young I feared disobeying my Dad. He only whipped me 3 times but they left a lasting impression. My first whipping was for jumping on my neighbor’s bed and breaking the slates underneath. The second was for shooting out all the windows in an old abandoned house in the woods with my new BB gun that I had gotten for Christmas. The lasting whipping was for egging cars.
But now that I am grown, I do not fear a whipping. I do fear displeasing him because of our relationship. Mature believers do not fear God breaking their legs for disobedience but a lost of closeness to their Heavenly Father. Next, Paul gives us a resulting mark of spiritual adulthood: Assurance of salvation.
4. Assurance of Salvation (8:16)
Paul only mentions two sources of witnesses in our lives (bearing witness is used only three times and only by Paul in Romans). Paul refers to our conscience twice and the Holy Spirit once bearing witness.
A. Our conscience bears witness in Romans 2:15 and 9:1-3.
The body is like the computer hard drive and the conscience is like the software. The conscience tells the body what to do and not to do by either accusing or excusing.
If we do wrong according to our conscience, it bears a witness by inflicting guilt. If we do what is right according to our conscience, it bears witness by excusing or remaining silent. This was Paul’s experience in 9:1-3 because his conscience was conditioned by the Word of God and the Holy Spirit. Conscience bears witness to what is there or not there. So is it with the Holy Spirit.
B. The Holy Spirit also bears witness in Romans 8:16 in relation to our salvation.
If there is obedience to the Word of God, the Holy Spirit bears witness. If there is a lack of obedience to the Word that is presented by a parent, friend, teacher or pastor, the Holy Spirit will not bear witness. The same is true if there is holiness of life and an intimate fellowship with God, the Holy Spirit bears witness. Finally, there is the mark of suffering in the all grown up man and woman of God.
5. An Inheritance of Suffering and Glory (8:17)
A. There is a present inheritance of Holy Spirit in 8:22 and 23.
B. There is a future inheritance of a glorified body in 8:17b.
“Adoption” is found five times in the New Testament. God the Father adopted Israel in the Old Testament (Romans 9:4), but God choose to adopt us before the foundation of the world (Ephesians 1:5). The Son paid for our adoption when he “redeemed them that were under the law that we might receive the adoption of sons” (Galatians 4:5). The Holy Spirit is the Spirit of adoption and also the Spirit of his Son who indwells us and enables us to cry like Jesus did to His Father, “Abba Father” (Galatians 4:6). Finally, our adoption has the future inheritance of a glorified body (Romans 8:17, 23).
C. There is also a present inheritance of suffering in 8:17.
During the Jim and Tammy Baker reign of their prosperity gospel they taught that God would make believers rich and prosperous. Tammy said, “When I tell God what car I want, I tell Him the color.”
Someone said our inheritance in this verse contains hurts and hallelujahs. Because we are co-heirs with Christ, who suffered before He reigned, so must we. The cross precedes the crown (James Montgomery Boice).
Part of the suffering as a child of God is chastening from our Heavenly Father according to Hebrews 12:5-11. The writer reminds us of our God’s Fatherly actions, “My son despise not the chastening of the Lord. For whom the Lord loves he chastens.” God wants His children to turn out well which requires discipline. Before Dad gave me my first spanking, he set me down and told me he loved me and that he was doing this for my good. After the spanking, he held me in his arms. How much more does our Heavenly Father love us and desire “the peaceable fruit of righteousness” in our lives.
Listen to Paul in 8:18: “For I reckon, or count it to be so, that the sufferings of this present time are not worthy to be compared with the glory which shall be revealed in us.”
 Warren W. Wiersbe, The Bible Exposition Commentary (Wheaton, IL: Victor Books, 1996), Ro 8:5.