1 Peter 5:8,9a NKJV - "Be sober, be vigilant; because your adversary the devil walks about like a roaring lion, seeking whom he may devour. Resist him, steadfast in the faith..."
Believers are to recognize that Satan has them in his "crosshairs." Satan hates Christians, especially those who are "on fire" for Christ. The devil is the adversary who is described as the "...accuser of our brethren, who accused them before our God day and night..." Revelation 2:10. Our Daily Verse and this passage in Revelation give us the two primary activities of Satan that he employs against Christians.
First, Satan seeks to "devour" believers. That word in Greek speaks of "drinking down" or "swallowing up." The thought is that Satan wants to "swallow up a believer's reputation and testimony." Satan can't have a Christian coming back into his kingdom, as much as he might wish he could. He will seek to upset the Christian and get the believer in a weak and vulnerable moment when he can attack him. That's why Peter encourages the believer to be "steadfast in the faith" so that the believer is strengthened in Christ to resist Satan. Remember, in James 4:7 we are told to "resist the devil" and the result will be his fleeing from us.
The second activity of Satan is probably what he is best known for: he is the accuser. His desire is to take a believer's testimony and basically ruin it. Satan can't actually make a believer sin, but he can bring accusations against a believer to sidetrack them from fruitful service for the Lord. Either other believers will listen to Satan's accusations, or the believers themselves will listen to his reminders of their past failures or their inability to face future challenges. How many Christians have avoided a possible fruitful ministry because they felt they just couldn't do it? That's part of Satan's accusations against them!
Believer, Satan is your enemy and you should be aware of his activities, but by no means do you need to live defeated lives. Christ has achieved victory for you and you are on the "winning side!" Resist the devil - he will run away!