A Grand Jury basically is a court trial where the Defense is not present at all. The Prosecution presents it's evidence and tells it's story without any arguments. The idea being that if the prosecution presents the best case it can and they still can't convince a jury to convict, then there is no real point to going to a trial. They are confidential in order to protect the defendant in the case that there isn't enough evidence to convict.
Ricknrockies t1_jedeb1e wrote
Reply to eli5 What does “indicted” mean? by jcw10489
A Grand Jury basically is a court trial where the Defense is not present at all. The Prosecution presents it's evidence and tells it's story without any arguments. The idea being that if the prosecution presents the best case it can and they still can't convince a jury to convict, then there is no real point to going to a trial. They are confidential in order to protect the defendant in the case that there isn't enough evidence to convict.