I don’t know whether or not you should shift careers; as a Christian, you should only do so after much prayer, and after you are convinced it is God’s will.
But I do know this: What you are doing is not worthless–not at all. After all, how much worse would our society be if we didn’t have people like you who are on the front lines combating crime? And how many individuals have you helped who were facing crisis situations–and would have had to face them alone if you hadn’t been there? The Bible says, “Blessed are they who maintain justice, who constantly do what is right” (Psalm 106:3).
Think of it this way: Are a doctor’s efforts useless just because people keep getting sick? Are a barber’s efforts useless just because people keep growing hair? No, of course not. And neither are your efforts, for as long as the human race exists society will have the same kind of problems you face every day. The reason is because we live in a fallen, sinful world, and human nature has not changed.
At the beginning of each day, ask God to help you, and to make you an encouragement to at least one person that day. Ask Him also to help you share Christ with your fellow officers. And please accept my sincere thanks for the fine work you and others like you do every day to make our world a safer and better place.