Satan hates you. Whether you believe in him or not, like him or hate him, or just try to not think about him, Satan hates you. Satan hates everybody, but he really, really hates people who try to do what God tells them to do because more than anyone else Satan hates God. The clash comes down to this: God wants people to follow Him to life, but Satan wants people to follow him to death.
Satan knows that he can't confuse God or cause God to doubt Himself. So the next best option is to go after God's followers. Satan tells people anything he can to get them to follow him. He doesn't care if he lies to you, if he tells you a half truth, or if he tells you a truth but in the wrong context. Lying is his favorite way to get you to start believing him and stop believing God. Satan doesn't really waste time bothering people who have "Christian" as a name tag yet don't really do anything for God. Those sort of "Christians" misrepresent God all on their own. Satan hates them but doesn't have a reason to get in their way. Instead Satan focuses his efforts on those trying to spread God's love and message of salvation. That means whenever you try to tell someone about God, Satan will try to tell you that the person didn't really pay attention and it was just a waste of time. It means that when you spend your time working to express God's love through helping someone, Satan will try to convince you that you didn't really help anybody and that person isn't thankful for it anyway. It means that no matter what you do for God, you will very likely encounter questions in your mind that cause you to doubt, to wonder, and to start to believe maybe this whole "working for God" thing doesn't really matter.
That is a lie. If the questions in your mind start to defeat you while you are working for God, step away from those doubts. Ask someone else for some perspective. Read your Bible for a little bit. Or just think back to what brought you to the place where you are at the moment. Very likely if you get out of your own head and away from where Satan can so easily ensnare you, you'll remember that everything is okay because God really is working, really does want you working with Him, and really is the salvation that everyone needs to hear about.
Remember, Satan says it doesn't matter, but Satan is also the one who hates you and will kick you in the face every chance he gets.