According to Jeremiah, this verse is about a time when he bought a piece of land and gave the proof of it to a man named Baruch, while making sure everyone saw it and knew it was true. This showed people that God would help them come back to their land one day.
Jeremiah 32:12: And I gave the evidence of the purchase unto Baruch the son of Neriah, the son of Maaseiah, in the sight of Hanameel mine uncle's [son], and in the presence of the witnesses that subscribed the book of the purchase, before all the Jews that sat in the court of the prison.
This verse emphasizes the importance of having many counselors or witnesses, implying that the giving of evidence to fewer people, as in Jeremiah 32:12, might lack the wisdom of collective advice.
Proverbs 11:14: Where no counsel [is], the people fall: but in the multitude of counsellors [there is] safety.