John Calvin Commentary Romans 8:16

"The Spirit himself beareth witness with our spirit, that we are children of God:" — Romans 8:16 (ASV)

The Spirit himself, etc. He does not simply say that God’s Spirit is a witness to our spirit, but he uses a compound verb. This verb might be translated as “contest” (contestatur), if it were not that “contestation” (contestatio) has a different meaning in Latin. But Paul means that the Spirit of God gives us such a testimony that, when he is our guide and teacher, our spirit is assured of God’s adoption. For our mind, by itself, without the Spirit's preceding testimony, could not give us this assurance.

This is also an explanation of the previous verse. For when the Spirit testifies to us that we are God’s children, he simultaneously pours such confidence into our hearts that we venture to call God our Father. And undoubtedly, since confidence of heart alone opens our mouth, unless the Spirit testifies to our heart about God’s paternal love, our tongues would be mute, unable to utter any prayers.

For we must always hold firmly to this principle: we do not pray rightly to God unless we are firmly convinced in our hearts that he is our Father when we call him so with our lips. Corresponding to this is the truth that our faith has no true evidence unless we call upon God. Therefore, it is not without reason that Paul, by bringing us to this test, shows that how truly anyone believes only becomes apparent when those who have embraced the promise of grace engage in prayer.

But here there is a striking refutation of the empty ideas of the Sophists regarding moral conjecture, which is nothing but uncertainty and mental anxiety; indeed, it is rather vacillation and delusion. This also answers their objection, for they ask, “How can a person fully know God’s will?”

This is certainly not something a person can achieve on their own; rather, it is the testimony of God’s Spirit. He discusses this subject more extensively in the First Epistle to the Corinthians, from which we can gain a fuller explanation of this passage.

Therefore, let this truth stand firm: no one can be called a son of God who does not know himself to be such. John calls this knowledge, in order to emphasize its certainty (1 John 5:19–20).