This is an intriguing promise, suggesting that believers can somehow inflict bruises on the devil, who is perpetually seeking to "devour" them (1 Peter 5:8). This promise is a clear allusion to the primeval assurance of Genesis 3:15, when God promised that the unique "seed" of "the woman" would eventually "bruise" (actually "crush") the head of the old serpent, the devil. This prophecy will finally be fulfilled in Christ's ultimate victory, when Satan first will be bound for a thousand years in the bottomless pit and then confined forever in the lake of fire (Revelation 20:2, 10).
In the meantime believers, who also in a sense are the woman's spiritual "seed" (Revelation 12:17), can repeatedly achieve local and temporary victories over Satan and his wiles by resisting him "stedfast in the faith" (1 Peter 5:9). If we resist him as Jesus did, with relevant Scripture, then God promises that he will "flee from you" (James 4:7). Such local victories can be obtained over these dangerous teachers whom Satan is using (note Romans 16:17-19, just preceding today's text) "shortly" in this manner, but we need to be continually alert against his recurrent attacks. The ultimate victory over Satan, of course, will be won only by the Lord Jesus when He returns, and we must "be sober, be vigilant" (1 Peter 5:8) until that time.
Whether we are aware of it or not, we must perpetually "wrestle . . . against the rulers of the darkness of this world" (Ephesians 6:12), who will be casting "fiery darts" (v. 16) against each believer. Finally, with the sword of the Spirit which is the Word of God (v. 17), we can even by God's grace inflict spiritual wounds on Satan himself! HMM http://www.icr.org/article/5970/