Jeremiah was a prophet (holy man). God chose Jeremiah as a prophet when Jeremiah was a young man (Jeremiah 1). Jeremiah lived at the same time as the last kings of Judah. Jeremiah warned the people that God would punish them (Jeremiah 4). They must return to God. Otherwise, they would suffer terrible troubles (Jeremiah chapters 14-16).
God wanted the people to trust him. But they refused (Jeremiah 18). So, God told Jeremiah that the people must serve their enemies for 70 years (Jeremiah 25). But then, people from Israel would return to their land (Jeremiah chapters 30-33).
Jeremiah also wrote about the future of other nations (Jeremiah chapters 46-51). And Jeremiah knew that God would send Jesus (Jeremiah 23:1-8, Jeremiah 31:31-37, and Jeremiah 33).
This Book is in the Old Testament section of the Bible.