The book of Malachi exposes Israel's corruption and also offers hope. Even after exile, their hearts are as hard as ever, but He will purify a faithful remnant and establish a New Jerusalem.
The entire Scripture is one unified story that tells us the truth about the human condition and sin while announcing God's promise to one day send a messenger and then show up personally. He will defeat evil and purify a faithful remnant, establish a New Jerusalem and bring peace, healing and justice forever. It's that promise that prompts God's people to denounce sin, remain faithful to His covenant and hope for the future.