Romans 8:16

The Spirit himself bears witness with our spirit, that we are the children of God:
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Ambrosiaster

AD 400
The witness of children is that by the Spirit they should be seen to bear the sign of the Father. Commentary on Paul’s Epistles.

Cyprian of Carthage

AD 258
Moreover, the blessed Apostle Paul exhorts and teaches, saying, "We are God's children; but if children, then heirs of God, and joint-heirs with Christ; if so be that we suffer with Him, that we may also be glorified together.". "We are "says he, "the sons of God: but if sons, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with Him, that we may also be glorified together.". And again: "We are children of God: but if children, then heirs; heirs indeed of God, but joint-heirs with Christ, if we suffer together, that we may also be glorified together.". Of this same thing to the Romans: "We are the sons of God: but if sons and heirs of God, we are also joint-heirs with Christ; if we suffer together, that we may also be magnified together."

Diodorus of Tarsus

AD 390
Paul showed by this that he called the soul “spirit” when it was spiritual, and the gift of the Spirit “Spirit.” .

John Chrysostom

AD 407
This means that the Comforter bears witness with the gift which he has given us. For it is not merely the gift which speaks but the Comforter who gave the gift as well.

Knowing this first, that no prophecy of the scripture is of any private interpretation - 2 Peter 1:20

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