8:16. For the Spirit himself giveth testimony to our spirit that we are the sons of God.
The Spirit himself, etc… By the inward motions of divine love, and the peace of conscience, which the children of God experience, they have a kind of testimony of God's favour; by which they are much strengthened in their hope of their justification and salvation; but yet not so as to pretend to an absolute assurance: which is not usually granted in this mortal life: during which we are taught to work out our salvation with fear and trembling. Phil. 2.12. And that he that thinketh himself to stand, must take heed lest he fall. 1 Cor. 10.12. See also, Rom. 11.20, 21, 22.
8:17. And if sons, heirs also; heirs indeed of God and joint heirs with Christ: yet so, if we suffer with him, that we may be also glorified with him.
8:18. For I reckon that the sufferings of this time are not worthy to be compared with the glory to come that shall be revealed in us.
8:19. For the expectation of the creature waiteth for the revelation of the sons of God.
The expectation of the creature, etc… He speaks of the corporeal creation, made for the use and service of man; and, by occasion of his sin, made subject to vanity, that is, to a perpetual instability, tending to corruption and other defects; so that by a figure of speech it is here said to groan and be in labour, and to long for its deliverance, which is then to come, when sin shall reign no more; and God shall raise the bodies and unite them to their souls never more to separate, and to be in everlasting happiness in heaven.
8:20. For the creature was made subject to vanity: not willingly, but by reason of him that made it subject, in hope.
8:21. Because the creature also itself shall be delivered from the servitude of corruption, into the liberty of the glory of the children of God.
8:22. For we know that every creature groaneth and travaileth in pain, even till now.
8:23. And not only it, but ourselves also, who have the firstfruits of the Spirit: even we ourselves groan within ourselves, waiting for the adoption of the sons of God, the redemption of our body.