I think the sins of the father, the pain of the mother, suffering of the poor, hunger, and pain are all references to painful things that he wants washed away or extinguished which is why he wants The Lord to make it rain. And "I know there can come fire from the sky, to refine the purest of kings" is a reference to the end of the world referenced in The Bible where fire is supposed to end the world this time and thus, all the pain, suffering, and sin will end, but he hurts so badly now that he just wants it to rain down deep within his soul to drown or flood all the pain away. The reference to lightning and thunder is just another way of him saying that he wants it to rain so hard that it washes it all away. Let me know what you think.