The Spirit Himself testifies with our spirit that we are God’s children.
16. The Spirit himself, etc. He does not simply say, that God’s Spirit is a witness to our spirit, but he adopts a compound verb, which might be rendered “contest,” (contestatur,) were it not that contestation (contestatio) has a different meaning in Latin.
In these verses the apostle represents two more excellent benefits, which belong to true believers. I. Life. The happiness is not barely a negative happiness, not to be condemned; but it is positive, it is an advancement to a life that will be the unspeakable happiness of the man (Rom 8:10, Rom 8:11): If Christ be in you. Observe, If the Spirit be in us, Christ is in us.
Commenting on Romans 8:10-16
The Spirit itself beareth witness,.... The thing which the Spirit of God witnesses to is, that we are the sons of God; which supposes the case in some sense doubtful and uncertain, at least that it is called in question; not by others, though it sometimes is, as by Satan, which need not seem strange, since he called in question the sonship of Christ himself...