“The Spirit itself beareth witness with our spirit, that we are the children of God.” (Romans 8:16)
Paul presents a magnificent section in Romans 8 on the resources of the believer. He begins with an affirmation that the Holy Spirit has been tasked to bear witness with our spirit that we are the actual children of God.
No less than 13 times does the phrase “children of God” appear in the New Testament, all written in one way or another to confirm that we “are all the children of God by faith in Christ Jesus” (Galatians 3:26).
Obviously, this does not apply to all humanity, as some would assert. None other than Jesus Himself stated that the wicked Pharisees and Sadducees were “of your father the devil” (John 8:44). The apostle John made the difference crystal clear: “In this the children of God are manifest, and the children of the devil: whosoever doeth not righteousness is not of God, neither he that loveth not his brother” (1 John 3:10).
The children of God are peacemakers (Matthew 5:9) and according to the Lord Jesus are “equal unto the angels” because they are “the children of the resurrection” (Luke 20:36). Furthermore, none other than the Creator Himself promises to “gather together in one the children of God that were scattered abroad” (John 11:52).
Finally, this is how each of us can know that we are, indeed, the children of God—“that we love the children of God, when we love God, and keep his commandments” (1 John 5:2). HMM III