Perhaps your law school professors were forgiving of your stylistic errors as long as they understood your arguments. If so, bear in mind that in many states the essays will be graded not by law professors, but rather by practitioners (lawyers and judges). When these attorney-graders read your essay, they are asking themselves only one thing: Is this someone I would want to deal with on a legal matter? If your essay answer is filed with sloppy language, sloppy reasoning and sloppy conclusions, they will conclude that you are not.
Ask any attorney practicing today and they will tell you that there is already a surplus of bad lawyers in the profession. Therefore, if you fail to communicate your answer in a lawyer-like fashion, you may remind the graders of all the terrible lawyers they are already dealing with on a day-to-day basis and they are going to want to weed you out now lest they end up sitting across from you someday on a legal matter and have to decipher your incomprehensible pleadings and correspondence.
On your bar exam essays, always write in full sentences and pay attention to spelling, grammar, and punctuation. Be sure that your answers are responsive to the questions asked and are based upon logical arguments. Make use of the IRAC method and always reason your way to a lawyer-like conclusion.
Do not forget that the bar exam is all about proving to the bar examiners that you are worthy of being granted admission to their profession.