There are several instances in the New Testament in which it speaks of people being possessed by demons. Such possession was manifested in a variety of ways. An individual may become blind (Mt. 12:22), unable to speak (Mt. 9:32), lame, mentally deficient (Mt. 17:15), possess unusual physical strength (Mk. 5:3-4), dropsy (Lk. 14:2), or even have epilepsy. Demons are special servants of the devil who inflicted mental and physical anguish on men during the first century. They only did harm and never anything good (Jn. 10:21). During his ministry the Lord manifested his power over the demonic world by casting them out of men (Mt. 17:18). The demons knew who Jesus was, the Son of God (Lk. 4:41). They even recognized his power over them as evidenced by the fact that some demons entreated him to cast them into a herd of swine and he granted their request (Mt. 8:31-32). The ultimate end of the devil and his angels is the eternal fire of hell (Mt. 25:41) and he wants to take as many as he can with him.
Several years ago the comedian Flip Wilson coined a phrase that became popular, "The devil made me do it." Anytime an evil deed was done it was attributed to the devil's influence as if that absolved man of all responsibility for the wrong committed. The interesting thing is that even during the period of time in which demons actually possessed man, you never read of their forcing a person to violate God's word against their will. Demon possession was always manifested in some mental or physical malady…never in causing a person to transgress the Lord's will. James said, "But each one is tempted when he is carried away and enticed by his own lust. Then when lust has conceived, it gives birth to sin; and when sin is accomplished, it brings forth death" (Jas. 1:14-15, emphasis mine). Thus, if we meet the Lord on the Day of Judgment in a lost condition, we can only blame ourselves. We can't even blame the devil.