And not only they - Not only the creation in general. “But ourselves also.” Christians.
Which have the first-fruits of the Spirit - The word used ἀπαρχὴ aparchē denotes properly the first-fruits of the harvest, the portion that was first collected and consecrated to God as an offering of gratitude, Deuteronomy 26:2; Exodus 23:19; Numbers 18:13. Hence, the word means what is first in order of time. Here it means, as I suppose, that the Christians of whom Paul was speaking had partaken of the first influences of the Spirit, or had been among the first partakers of his influences in converting sinners. The Spirit had been sent down to attend the preaching of the gospel, and they were among the first who had partaken of those influences. Some, however, have understood the word to mean a pledge, or earnest, or foretaste of joys to come. This idea has been attached to the word because the first-fruits of the harvest were a pledge of the harvest, an evidence that it was ripe, etc. But the word does not seem to be used in this sense in the New Testament. The only places where it occurs are the following; Romans 8:23; Romans 11:16; Romans 16:5; 1 Corinthians 15:20, 1Co 15:23; 1 Corinthians 16:15; James 1:18; Revelation 14:4.
Groan within ourselves - We sigh for deliverance. The expression denotes strong internal desire; the deep anguish of spirit when the heart is oppressed with anguish, and earnestly wishes for succor.
Waiting for the adoption - Waiting for the full blessings of the adoption. Christians are adopted when they are converted Romans 8:15, but they have not been yet admitted to the full privileges of their adoption into the family of God. Their adoption when they are converted is secret, and may at the time be unknown to the world. The fullness of the adoption, their complete admission to the privileges of the sons of God, shall be in the day of judgment, in the presence of the universe, and amidst the glories of the final consummation of all things. This adoption is not different from the first, but is the completion of the act of grace when a sinner is received into the family of God.
The redemption of the body - The complete recovery of the body from death and corruption. The particular and striking act of the adoption in the day of judgment will be the raising up of the body from the grave, and rendering it immortal and eternally blessed. The particular effects of the adoption in this world are on the soul. The completion of it on the last day will be seen particularly in the body; and thus the entire man shall be admitted into the favor of God, and restored from all his sins and all the evil consequences of the fall. The apostle here speaks the language of every Christian. The Christian has joys which the world does not know; but he has also sorrows; he sighs over his corruption; he is in the midst of calamity; he is going to the grave; and he looks forward to that complete deliverance, and to that elevated state, when, in the presence of an assembled universe, he shall be acknowledged as a child of God. This elevated privilege gives to Christianity its high value; and the hope of being acknowledged in the presence of the universe as the child of God - the hope of the poorest and the humblest believer - is of infinitely mere value than the prospect of the most princely inheritance, or of the brightest crown that a monarch ever wore.