One reason is that I honestly believe that teaching my law students about ancient lawyers and lawyering is a worthwhile enterprise in itself, not necessarily because "origins" are special, but because the exercise expands the mind by forcing us to contemplate how legal and social norms were articulated and defended in cultural contexts radically different from our own. If the past is a foreign country, the distant past is even more so, and from a humanistic or anthropological perspective I think exploring that past is a good thing. Secondly, I believe ancient lawyers can usefully remind us of the deep connection between advocacy and community, and how the former can serve and improve the latter by persuasive appeals to shared values through responsible rhetoric (thus Quintilian's famous definition of the true orator as a "good man speaking well"). Frankly, I'd take a few pages from Cicero or Quintilian on this topic over most contemporary legal ethics textbooks any day of the week.
Thirdly, I want my law students to understand that lawyering in America did not appear full-blown and immaculate, like (to pointedly use a simile from ancient Greek mythology) Athena springing from the forehead of Zeus. Eighteenth, nineteenth and even a few (mostly early) twentieth century American lawyers overtly saw themselves as heirs of the (legal) ancients. John Adams (whom Daniel Coquillette cleverly called "Justinian in Braintree" at one point) routinely evoked Cicero; James Kent admired Juvenal; Daniel Webster imitated Demosthenes; Rufus Choate translated Quintilian for pleasure; William Wirt had his portrait painted in classical garb; Elihu Root bought busts of both Cicero and Demosthenes for his personal library. It's interesting how the popularity of certain ancient lawyers and rhetoricians ebbed and flowed over time as American political and legal circumstances changed. Roman legal figures seem to have dominated the legal thinking and oratory of the Revolutionary era. Greek orators like Demosthenes were more often evoked in the courtrooms and legal classrooms of Jacksonian America, and then interest in the Roman (and this time largely imperial) legal past gained ground again as America became a world power in the late 19th century. Go figure. Only in the 20th century, when the underpinning of classical undergraduate education and classical languages was largely lost, even to the upper end of the bar, did "ancient lawyers" lose their fascination for the American legal mind.
Of course there's another problem here. Are the men I've mentioned - the Greeks and the Romans, that is - really ancient "lawyers" at all? Many scholars these days might take issue with early twentieth century classicist Robert J. Bonner, the author of Lawyers and Litigants in Classical Athens, but yet we must acknowledge that even in the fourth century BCE orator-logographers like Demosthenes and Lysias performed lawyer-like functions when writing speeches for litigants, and occasionally standing up before juries as synegoroi (loosely "friends" or character-witnesses) for vulnerable or disabled parties. We could also quibble about whether Cicero the advocate saw himself as any kind of lawyer (objective evidence aside, there's evidence in Cicero's De Oratore to suggest he would have been insulted by the allegation). We seem to be more comfortable characterizing Roman jurists like Ulpian and Tribonian as lawyers, but that may say as much about us and our contemporary legal biases towards writing and writers as it does about them. One way to get around the entire problem is by minimizing and dodging it - in my case, saying at the outset that my course is about the history of "lawyering", a gerund that embraces multiple activities conducted at various junctures by lawyers (and others) without being necessarily confined to individuals who pass some kind of occupational litmus test. This focus on activity rather than arbitrary occupation comes in handy at later junctures in the course, allowing me to talk about people and groups who have worked in lawyerly capacities (often challenging or supplementiung lawyers) without claiming to be lawyers themselves, i.e. social workers in the late 19th century, paralegals in the late 20th, and so on.
At the end of the day I only spend a total of three classes out of 24 on ancient lawyers and lawyering. These classes are but a gesture, a nod to a much larger and more complex legal and (if you like) professional past. But I'm glad I offer them. Some of my initially-hesitant law students discover that they actually *like* the "lawyers" I present (Cicero in particular, it seems), and the introductory coverage I provide here helps to draw them into my Ancient Law seminar. Others find they can relate to the early criticisms of advocates offered up by legally-disinclined Roman poets such as Martial and Horace, whose ancient quips at our lawyerly expense help humanize the otherwise dusty old busts of the "greats." But in this part of my course it's Cicero who has the last word. Murdered by the agents of Anthony in an act that marked the ultimate failure of advocacy in the Roman Republic (all the more so because Cicero's head and hands ended up being nailed to the Rostrum), I remind my students of his verdict on the value of history: "To be ignorant of what occurred before you were born is to remain always a child." I hope that learning about Cicero and other "ancient lawyers" helps my law students to grow up.