A Diabolo (The Devil)
The Devil is known by many names in Scripture: Satan, Great Dragon, the Devil, Belial, god of this world, prince of the power of the air, etc. His three main goals seem to be to slander (to question motive or imply wrong-doing such as he did to Job [1-2]), to accuse (to point out all the wrong we do before God and to ourselves [Zech 3.1; Rev 12.10]), and to seduce (as he did David [1 Chron 21.1; 2 Thess 2.9-10; Rev 13.3-4]). He is cosmically powerful and even the archangel Michael, captain of the host of God's angelic army, rebukes Satan only in the name of the Lord (Jude 9).
However, Satan has limitations. He is not God's equal in any way because he is a created being. He has to ask permission before he can do anything to God's people (Job 1.12, 2.6; Lk 22.31). He is a fallen being and therefore judged (Lk 10.18; Jn 16.11); his power over people can be broken (Acts 26.18). His temptations can be seen through and overcome (Matthew 4.1-11). He can be resisted (Eph 4.27; Jms 4.7; 1 Pet 5.8-9) because he is only a prince in this world (Jn 12.31; Eph 2.2). God controls his binding, releasing, and perpetual incineration (Revelation 20).
Because he is a cosmic being, he is stronger than we are and has abilities that exceed us. Because he has limitations, he has to have our help to defeat us. Our "Achilles Heel" is summed up in one question: What are we willing to do to get what we want? Louis Sweet wrote in the International Standard Bible Encyclopedia that "Men are not tempted by evil, per se, but by a good which can be obtained only at the cost of doing wrong." Sex is a good, but many times obtained by wrong means (unmarried, adulterous, homosexual, etc.).
There are three stages one reaches when descending into darkness. Sifting (Lk 22.31) is when Satan offers us choices to see what we will be willing to do to get what we want (2 Thess 2.10-12; Jms 1.14). When Satan sees that we are willing to at least consider wrongdoing to get what we want, he then fills our hearts (Acts 5.3; Jms 1.15; Eph 2.3). He fills our minds/hearts with the desire for the thing, so that we will do whatever it takes to get it. Sometimes we get so used to giving in to temptation, we give in without conscious thought. The third stage is when Satan enters our hearts (Lk 22.3; Jn 13.27; Eph 2.2; Jn 9.44). At this stage, questions of possession are irrelevant. We become his tool for evil, his possession. He owns us.
However, Paul tells us of three things that will protect us from Satan in Ephesians 6.10-12. First, we must be strong in the Lord (10). The better F.R.I.E.N.D. we are of God, the less vulnerable we'll be. I preached a sermon on being God's F.R.I.E.N.D. on the last Sunday of September. Second, Paul says to put on the armor of God (11). This is truth, righteousness, preparation, faith, salvation, the word of God, and prayer. It is similar to Peter's list in 2 Pet 1.5-11, where Peter says "For if you do these things, you will never fall." Third, take your stand against darkness (11-12). That involves being self-controlled, alert, and resisting (1 Pet 5.8-9). The deeds of darkness are found in many Scriptures, but Gal 5.19-21 is a good place to start. To take your stand against something is to denounce it when it appears, to protect yourself from it, and to help others see the danger in it. You cannot really stand against something when you are dabbling with or diving into it.

~Shawn