What does Romans 8:16 mean?

Paul has written in the previous verse that it is by God's Holy Spirit, given to us by God when we became His children through faith in Christ, that we call out to God as "Abba" or Father. Paul gave another name to the Spirit: "Spirit of adoption." God adopted us into His family.

Bit by bit, Paul is revealing exactly what the Holy Spirit does in and through those who are in Christ. In Romans 8, he emphasizes that communication between us and God is one of the key works of God's Spirit in us. That communication goes in both directions. By the Spirit, we can communicate with God at the most basic level. We cry to Him and He hears from us "Abba! Father!" Romans 8:26–27 goes even further, showing that the Spirit is the one who takes our prayers, even when we don't know what to pray, to the heart of our Father.

In this verse, the communication goes the other way. God communicates from His Spirit to our spirit that we are His children. His Spirit "bears witness," keeps communicating to us over and over that we belong in God's family now that we are in Christ. He confirms to us what is true on some deep and unspoken level.

The confidence we carry that we belong to God, not because of our goodness or effort but because of His love for us, comes directly from God's Spirit with us.