[from Commentary on Romans 8:14...] The import of the whole is this — “all those are the sons of God who are led by God’s Spirit; all the sons of God are heirs of eternal life: then all who are led by God’s Spirit ought to feel assured of eternal life. But the middle term or assumption is omitted, for it was indubitable. But it is right to observe, that the working of the Spirit is various: for there is that which is universal, by which all creatures are sustained and preserved; there is that also which is peculiar to men, and varying in its character: but what he means here is sanctification, with which the Lord favors none but his own elect, and by which he separates them for sons to himself.
[from Commentary on Romans 8:16...] But Paul means, that the Spirit of God gives us such a testimony, that when he is our guide and teacher, our spirit is made assured of the adoption of God: for our mind of its own self, without the preceding testimony of the Spirit, could not convey to us this assurance. There is also here an explanation of the former verse; for when the Spirit testifies to us, that we are the children of God, he at the same time pours into our hearts such confidence, that we venture to call God our Father.
[from Commentary on 1 Corinthians 2:12...] It is a passage that is most abundantly clear, for refuting that diabolical doctrine of the Sophists as to a constant hesitancy on the part of believers. For they require all believers to be in doubt, whether they are in the grace of God or not, and allow of no assurance of salvation, but what hangs on moral or probable conjecture. In this, however, they overthrow faith in two respects: for first they would have us be in doubt, whether we are in a state of grace, and then afterwards they suggest a second occasion of doubt — as to final perseverance. Here, however, the Apostle declares in general terms, that the elect have the Spirit given them, by whose testimony they are assured that they have been adopted to the hope of eternal salvation. Undoubtedly, if they would maintain their doctrine, they must of necessity either take away the Spirit of God from the elect, or make even the Spirit himself subject to uncertainty. Both of these things are openly at variance with Paul’s doctrine. Hence we may know the nature of faith to be this, that conscience has from the Holy Spirit a sure testimony of the good-will of God towards it, so that, resting upon this, it does not hesitate to invoke God as a Father