Isaiah prophesied around 740-680 B.C. He prophesied during the reigns of Uzziah, Jotham, Ahaz, and Hezekiah. Isaiah was a contemporary of Hosea and Micah. He prophesied during the last days of the Northern Kingdom, but his message was largely to Judah (Southern Kingdom) telling them they would likewise perish if they didn't straighten up.
Jeremiah prophesied about 100 years later (around 627-580 B.C.). He prophesied during the last days of the Southern Kingdom (because they hadn't straightened up). Jeremiah was a contemporary of Zephaniah, Habakkuk, Daniel, and Ezekiel. His ministry can be divided into three stages:
Jeremiah 1-33 - Before the Fall of Judah
Jeremiah 34-45 - The Fall of Judah
Jeremiah 46-52 - After the Fall of Judah
Jeremiah was young when God called him in chapter 1. He protested, "Alas, LORD GOD! Behold, I do not know how to speak, Because I am a youth" (Jer. 1:6). But God gave him strength and effectively equipped him for the service he was to render. He told Jeremiah, "Do not be afraid of them, For I am with you to deliver you" (Jer. 1:8). Whenever God calls someone to a specific service, He always fully equips them for the service and is a source of strength and comfort.
Chapter 2 - Judah leaves the LORD and God gives them into the hands of the nations (Egypt and Assyria - v. 18, 36). But it's their own doing (v. 17, 19).
In Chapter 3 God divorced Israel (the Northern Kingdom) because of her harlotries. He expected Judah to learn from her sister in the north, but she did not. She committed the same harlotries with idols. Jeremiah 3:11 says, "Faithless Israel has proved herself more righteous than treacherous Judah." Ouch. God just wanted a Father-son relationship with Judah (3:19-20). Why do we have to make it so difficult for God? Why are we always fighting against Him instead of with Him? Why are we so fickle? God is so merciful to us - let's revel in His mercy and enjoy Him!
Nathan