Satan is our great enemy, he is not always after those that are not saved because he knew they are his own already but he is after those that are saved. he is set to entice us with those things that did not worth it just to steal our heart and faith in god but there is nothing good that he can offer without getting the best from us.
He is out there to kill and to destroy but we have a choice through the grace of God and the help of Holy Spirit not to allow him in our heart.