See how Jeremiah prayed in Lamentations 5. He told God exactly what was going on in Jerusalem. "Remember, O LORD, what has befallen us; Look, and see our reproach!" he said in Lamentations 5:1. It's not as if God didn't already know the score - after all, He brought this punishment upon Jerusalem. So why did Jeremiah, in this prayer, spend most of the chapter explaining to God the plight of Jerusalem?
Doesn't God already know everything we are going to ask before we ask? So why ask? Why tell God anything if He already knows? For one thing, God wants us to express our feelings and issues to Him. It's good for us, it's true, but it is COMMUNICATION. God wants a relationship with His creation. Relationships are built around communication. Jeremiah understood this. He didn't just say, "Lord, You can see everything that's been happening here, so please save us." He went into great detail REMINDING God of Israel's situation.
It's significant he ended the poem with: "Restore us to You, O LORD, that we may be restored; renew our days as of old, unless You have utterly rejected us and are exceedingly angry with us" (Lamentations 5:21-22). This reflects God's entire plan of salvation. God restores!
Nathan