The origin of the jury goes back quite a long time; originally, they were the people that knew the plaintiffs / defendants and in theory would know the background to the case. It was assumed that these people would be the best ones to provide the judge with the details needed to decide a claim.
However, over the years, that has changed and now the jury is meant to be an impartial group selected from the public, that can hear the evidence and make a decision based upon that alone. In many cases, because they are lay people, they will not be aware of the minutiae of the law; which is why the court can provide them with guidance or even direct them to pay specific attention to / ignore certain information.
However, it appears that far too many of the individuals selected to carry out jury duty these days, don't have the basic common sense required to perform this civic function. (OK, many of them are as thick as s***.) There's been an argument that perhaps we need to have a group of people that would be "professional" jurists from which a jury of 10 or 12 would be selected. The idea is then that they might be better equipped to handle the specific requirements of the function.
I'd previously not been too happy about the concept; I can see too many ways in which it could be abused. But perhaps it is time to rethink this; quite simply, there are just too many cases where the individual jurists have ignored the information provided, or have been influenced by something they had read / seen (especially some the court room dramas whcih are usally so bloody inaccurate, they make the legal profession scream in frustration).