Every jury trial begins with voir dire and selection of the jurors who will decide the disputed issues of fact. It is during this time that the jurors begin to learn what the case is about; what facts may be presented. The first opportunity a lawyer has to fully present the facts to those jurors, however, is opening statement. Though it may seem like it should go without saying, the opening statement should be just that; a statement about what facts will be presented (or not presented) during the trial. It should not be the time to argue or try to urge jurors to draw inferences from the facts (though most good openings present a statement of the facts in a manner that feels like it is argument even though it is not). That being said, at a trial seminar I attended in the last several months there was much debate over how much arguing about the facts a lawyer should do in opening statement.
One viewpoint was that you should argue as much as the opposing lawyer allows you to. Another view was that no argument is ever appropriate. In practice it seems most lawyers fall somewhere in between these two views. It seems to me that most lawyers at least attempt to avoid arguing too many points in their opening but still end up advocating one way or another through argument. And, most lawyers seem to let some argument pass without objection. Nonetheless, most good openings avoid outright argument before the jurors have heard a shred of real, admissible evidence. Rather, most good openings skillfully tell a story which gets the jurors thinking about the case from the desired perspective.