Chapter 28--A false prophet (Hananiah, the son of Azur the prophet) prophesied that God had broken the yoke of Babylon already, and within 2 years: 

• all the vessels from the Lord's house would be returned
• Jeconiah (the son of Jehoiakim, the king of Judah) would return to Jerusalem
• all the captives would return to their land

    Jeremiah responds to this prophecy in the presence of the priests & all the people who stood in the house of the Lord.  He states that if indeed the prophecy comes true...that he would "Amen" the prophet.  However, in times past...prophets were given the responsibility of telling "bad" news.  They were often despised by the people.  On the other hand, the prophet who delivers news of "peace" will be revered by all.  
    Jeremiah was implying that people would rather hear good news than bad.  Because the message is good news, the people will regard Hananiah highly...when it comes to pass.  However, he was also implying that he (Jeremiah) was going to wait until the peace comes...before he begins applauding the prophet!
    Jeremiah got the last word in.  He told hananiah that he was a false prophet & a liar.  And because of his actions, he was going to die this very year.  And he did!

Note:  People are notorious for believing those who tell us what we want to hear...rather than what we need to hear.  This is true whether the speaker is a prophet, preacher, ...or a politician!  Messages are given & promises are made that people want to hear (even though there is no way that they can all come true)...just so people will follow them.
   In the case of Jeremiah, no one wanted to hear a message on God's judgment...they wanted to hear about peace & prosperity.  In today's society, people are the same way.  "Tell them what they want to hear."   In the case of politicians, once elected they can blame someone else for unfulfilled promises! 

Chapter 29--Some of those who were taken away into captivity may have heard of the false prophecy claiming that they would be returning home soon.  God directs Jeremiah to write a letter to them telling them to begin living in their new land as though they were going to be they a long time.  He wrote:

• build houses and dwell in them
• plant gardens & eat their fruit
• marry & have children
• get wives for your sons & husbands for your daughters (so they can have children & continue the lineage)
• pray for peace in the place that you are dwelling now

    In the middle of this letter of encouragement to the captives in Babylon, God writes..."For I know the plans I have for you,' declares the Lord, "plans to prosper you and not to harm you, plans to give you hope and a future.  Then you will call upon Meand come and pray to Me, and I will listen to you.  You will seek Me and find Me when you seek Me with all your heart"  (vv.11-13). 

Note:  God didn't change the judgement He pronounced upon the house of Judah, but He reassured them that He hadn't abandoned them.  He gave them a plan of action...and a hope for the future. 

Chapter 30--Jeremiah is told to put in a book...all that was given to him by God.  (I assume that the Book of Jeremiah is the resulting book that God was talking about.)  God continues His declaration that His judgment upon the people of Judah will continue as planned...but that there is light at the end of the tunnel. 
     In all that was said, the most comforting word is found in v. 22, "You shall be My people, and I will be your God."