Albert Barnes Commentary Romans 8:16

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

The Spirit: The Holy Spirit. That the Holy Spirit is intended here is evident,

1. because this is the natural meaning of the expression;
2. because the apostle is mainly addressing the Holy Spirit in this passage;
3. because it would be an unnatural and forced interpretation to say that the disposition of adoption itself bore witness.

Bears witness: Testifies, gives evidence.

With our spirit: To our minds. This pertains to adoption, meaning that the Holy Spirit furnishes evidence to our minds that we are adopted into the family of God. This effect is not infrequently attributed to the Holy Spirit (2 Corinthians 1:22; 1 John 5:10–11; 1 Corinthians 2:12).

If it is asked how this is done, I answer: It is not by any revelation of new truth, not by inspiration, not always by assurance, and not by a mere persuasion that we are elected to eternal life. Rather, it is by producing in us the appropriate effects of His influence.

It is His work to renew the heart, to sanctify the soul, and to produce love, joy, peace, long-suffering, gentleness, goodness, faith, meekness, temperance (Galatians 5:22–23).

If a person has these qualities, they have evidence of the Spirit witnessing with their spirit. If not, they have no such evidence.

Therefore, the way to determine whether we have this witnessing of the Spirit is by an honest and prayerful inquiry into whether these fruits of the Spirit actually exist in our minds.

If these fruits do exist in our minds, the evidence is clear. If not, all vain confidence of a good spiritual state, all visions, and raptures, and fancied revelations will be mere delusions.

It may be added that the effect of these fruits of the Spirit on the mind is to produce a calm and heavenly frame of mind. In that state, when accompanied by the appropriate fruits of the Spirit in a holy life, we may rejoice as an evidence of piety.

That we are the children of God: This means that we are adopted into His family.