Romans 16:20; "And the God of peace will crush Satan under your feet shortly. The grace of our Lord Jesus Christ be with you. Amen."
John Calvin's comments
"What follows, God shall bruise Satan, &c., is a promise to confirm them, rather than a prayer. He indeed exhorts them to fight manfully against Satan, and promises that they should shortly be victorious. He was indeed once conquered by Christ, but not in such a way but that he renews the war continually. He then promises ultimate defeat, which does not appear in the midst of the contest, At the same time he does not speak only of the last day, when Satan shall be completely bruised; but as Satan was then confounding all things, raging, as it were, with loose or broken reins, he promises that the Lord would shortly subdue him, and cause him to be trodden, as it were, under foot. Immediately a prayer follows, — that the grace of Christ would be with them, that is, that they might enjoy all the blessings which had been procured for them by Christ."
Calvin affirmed that Satan would soon be subdued. It was a first century event. Subdue is to "overcome, quieten, or bring under control." The reformer understood that Christ ultimately defeated Satan and all powers and dominions at Calvary (Colossians 2:15). Calvin was not inferring that there would be immediate peace and the institution of an instant, mature kingdom. No, the complete defeat of Satan will be fulfilled or finalised on the last day. God's beloved world is to be discipled before then (Matthew 28:18-20).
John Calvin was clear that Satan was subdued in the first century. There was a mini head crushing. The Roman Christians would crush Satan under foot shortly. This is a time text indicator. "Shortly" cannot mean thousands of years later. Even though the devil rages, he has been chained and restrained (James 4:7, Revelation 20:1-3). His power was subdued by Christ and his head was trampled on by the early church. A head trampling was a sign of being defeated and subdued. The Gentile nations of this world were removed from under Satan's dominion and given to Jesus as His inheritance (Psalm 2, Hebrews 1, Matthew 28:18-20). The Messiah's death, resurrection and ascension accomplished this. All the nations of this world now belong to Christ (Psalm 2 - cf. Hebrews 1, Matthew 28:18-20, Revelation 11:15.
Note also that the head stomping was not through the power of autonomous man or church. The God of peace is whose power enables the church to stand in faith and pound on the head of Satan. Often this head stomping came through great trial and tribulation.
This armed the church with Gospel confidence to go out into all the world and disciple all the nations. Why? All the nations of the world now belonged to Jesus. The church could now go out to the ends of the world and herald that the new King had come. Messiah was enthroned at the right hand of the Father and now ruled the world. They could proclaim that Jesus had established His kingdom across every nation (Matthew 28:18-20) and that He commands all of His subjects (i.e. all people) to repentance, belief and faithful obedience (Acts 17:30, John 3:16, 1 John 5:1-5). Christianity never established the kingdom on earth, Jesus did. The church is to proclaim the reign, authority and crown rights of King Jesus over every square inch of life and the world. All things are to be conformed to the new King (2 Corinthians 10:5) and His Law (Matthew 28:20).
Calvin's comments on Romans 16:20 affirmed that the church was amidst a raging battle. Calvin affirmed that Biblically the penultimate war had been won at Calvary; and the Christians of the first century were to take courage as the battle was shortly to be won by them stamping on Satan's head. This is not a defeatist Gospel. Christ is victorious and reigns with all power and authority. His church will disciple the nations while Satan is subdued. Christ will not return until the Gospel has gone out and the nations are discipled.
The Gospel is victorious and triumphant.