Paul uses a metaphor to compare a person who refuses to obey God to something hard, like a stone. He also uses the metonym "heart" to represent the person's mind or inner being. Alternate translation: "It is because you refuse to listen and repent" (See: [[rc://en/ta/man/jit/figs-metaphor]] and [[rc://en/ta/man/jit/figs-metonymy]])
The phrase "storing up" implies a metaphor that usually refers to a person gathering his treasures and putting them in a safe place. Paul says, instead of treasures, that the person is gathering God's punishment. The longer they go without repenting, the more severe the punishment. Alternate translation: "you are making your punishment worse" (See: [[rc://en/ta/man/jit/figs-metaphor]])
Both of these phrases refer to the same day. Alternate translation: "when God will show everyone that he is angry and that he judges all people fairly" (See: [[rc://en/ta/man/jit/figs-doublet]])