the opening arguments by both sides are to outline what they will prove during the case. They give a vague outline of how they intend to do this. they outline evidence, witnesses, timelines, and they try to give a view as to the defendants/arrestees for doing or not doing something without creating too much expectation for their side but the opposite for the other side.

Obviously the motive of the prosecutor is to prove the perpetrator is guilty beyond a shadow of a doubt. Proving it by the evidence that is given . The defense attorney is hired or if the accused doesn’t have the money for a lawyer,he/she is given a court-appointed attorney. The defense lawyer also has to prove the innocence of his client given the details and evidence or lack off to the appeal of the jury and/or the judge. From the opening statements they both will attempt and name the defendent and the charges against him or her and then go on to try to prove their case beyond a reasonable doubt. They appeal to the judge and to a jury if present.

Opening arguments are to set the stage for what they intend to do in the defense and/or prosecution in the specific case.

So they can get the jury in the frame of mind they want to be able to convince them of their point of evidence.