For we know that the whole creation has been groaning together in the pains of childbirth until now.
22. For we know, etc. He repeats the same sentiment, that he might pass over to us, though what is now said has the effect and the form of a conclusion; for as creatures are subject to corruption, not through their natural desire, but through the appointment of God, and then, as they have a hope of being hereafter freed from corruption, it hence follows...
In these words the apostle describes a fourth illustrious branch of the happiness of believers, namely, a title to the future glory. This is fitly annexed to our sonship; for as the adoption of sons entitles us to that glory, so the disposition of sons fits and prepares us for it. If children, then heirs, Rom 8:17.
Commenting on Romans 8:17-25
For we know that the whole creation groaneth,.... As a woman with child, ready to bring forth: for it is added, and travaileth in pain together until now; regeneration is owing to the grace of God, which is compared to "seed", of which men are born again; the means of conveying it is the Gospel, and ministers are the instruments of begetting souls to Christ...