This is a wonderful article on the current state of the Devil by a postmillennialist. It can be read in full here. And I certainly recommend a complete reading of the article to understand both the amillennial and postmillennial view that Satan has been bound since the first advent of Jesus Christ.
In this blog I'm going to quote and highlight the description of Satan in 1 Peter. I intend on teaching through 1 Peter next year and found this insightful. Greg says the following (emphasis added),
Another central activity of Satan is the slandering of God's people (Rev. 12:10); he brings false accusations against them in order to see to their spiritual death. Thus he is a murderer (John 8:44). But his murderous designs extend beyond the spiritual realm to the physical world as well. As well as delivering slander, the devil creates persecution for the godly. When the Jews sought to kill Jesus (John 8:40-41), He said that they were following the desires of their father the devil, who was "a murderer from the beginning" (vs. 44) referring to the diabolical origin of Cain, who murdered his brother (I John 3:12). Satan inspires persecution and martyrdom for Christians (Rev. 2:9-10). Knowing that his time is short, Satan operates on earth with great wrath (Rev. 12:12). Therefore, Christians must be serious and alert about Satan (I Pet. 5:8), for their "adversary walks about as a roaring lion, seeking whom he may devour." Satan traverses the earth and has access to us (cf. Job 2:2). Many commentators have misinterpreted the allusion in I Peter 5:8 by overlooking the fact that it is Satan's walk (not himself personally) that is likened to a lion, and by failing to take cognizance that it is a roaring lion (not a stealthily stalking lion) that Peter takes for comparison to Satan's walk. Satan is not himself a lion, but his walk or behavior in the world can be likened to the walk of a roaring lion. A roaring lion was an Old Testament symbol for savage opposition and one's enemies (Ps. 22:13-14; Prov. 28:15; Isa. 5:29; Zeph. 3:3); to be "saved from the lion's mouth" was a figure for deliverance from one's persecutor (Ps. 22:21; II Tim. 4:17). Lions do not roar when sneaking up on their prey (for obvious reasons); instead, they roar in order to instill fear and to express a ferocious nature (e.g., Judges 14:5) or as part of a vicious attack upon an intruder (e.g., Dan. 6:22). Thus the lion's roar was metaphorical for the wrath and threat of a monarch (Prov. 19:12; 20:2). In I Peter 5:8, we do not see Satan represented in his secret and subtle activities as the adversary of God's people; we see him as the ferocious threat brought by persecutors (especially political oppressors) against believers. Peter explains the threat of the roaring lion as "sufferings" in the next verse, and in 4:12 he had forewarned his readers of the "fiery trial" that was soon to descend upon them. As a lion seeks someone to devour, so Satan walks through the earth activating physical persecution against Christians. He would try to drive them to faithlessness and apostasy through the violent opposition he engenders. In the short time that he has left to him, Satan expresses great wrath against God's people. If he cannot destroy them by deception, he aims to destroy them (spiritually) through fear, or to destroy them (physically) through martyrdom.
So how is Satan "walking around" today? Through materialism, humanism and the general acceptance of the world's culture. When the Church refuses to reject the behavior of the world, it bends into a passive denial of Christ's Lordship and Satan has succeeded.
The upholding of Christ as Lord is what defeats Satan. And this is exactly what James says, "Submit to God...Come near to God" (Jam 4:7-8).