My Brother Is Acting Crazy. He Is Saying Irrational Things,

My brother is acting crazy. He is saying irrational things, like he is God. He says he doesn't need money and that he will give all his money away. He is 21. One minute he's happy and the next he's really depressed. He says he is connected to inanimate objects and he thinks he was put on this earth to save everyone. He said he will kill himself in a month if he does not complete his "mission". I'm really concerned but he won't agree to go to a psychiatrist. Idk what to do.