The answer is: Malachi

Malachi 1:1 - As the final book of the Old Testament, Malachi serves as a bridge to the New Testament, addressing issues of spiritual apathy and God's love. Interestingly, Malachi mentions the coming of Elijah before "the great and dreadful day of the Lord" (Malachi 4:5), which connects to John the Baptist in the New Testament (Matthew 11:14).

Malachi, the final prophet in the Old Testament lineup, packs quite a punch in just a few short chapters! Authored around the fifth century BCE, during a time of restoration after Israel's exile, the book isn’t just a closing note but a critical reflection on the state of the people. Can you imagine being one of the returnees and hearing a prophet challenge you about your lukewarm sacrifices? That's the flavor of Malachi, where God reminds the Israelites to bring their best, specifically in 1:8, urging them to offer unblemished sacrifices—something scholars suggest was crucial for maintaining devotion.

What’s even cooler is the echoes of God’s connection to humanity throughout Malachi. When the prophet speaks of God’s love for Israel, a theme echoed in many other books, it emphasizes a recurring biblical motif: the idea that love compels faithfulness. God's call for the Israelites to return to Him arises multiple times in scripture, reinforcing that the relationship is mutual—the divine longs for connection!

And let’s not overlook that tantalizing promise about Elijah's return, either. This prophecy has enriched Jewish and Christian thought alike, expressing deep anticipation for future redeeming acts. There’s a rich tapestry woven through Malachi—linking the love of God, the specific call for worship, and acts of faith that threads not just between testaments but through the hearts of those wrestling with their faith today.