When thou sittest to eat with a ruler. This, of course, would be a great honour to a man of lowly birth, or to one of the middle class, to whom the manners of courts and palaces were practically unknown.
Consider diligently what is before thee. So the Vulgate, Qua apposita sunt ante faciem tuam; and the Septuagint, τὰ παρατιθέμενά σοι. Take heed lest the unusual dainties on the table tempt thee to excess, which may lead not only to unseemly behaviour, but also to unruly speech, revealing of secrets, etc.
But the latter words may also be tendered, "him that is," or, "who is before thee." And this gives a very appropriate sense. The guest is enjoined to fix his attention, not on the delicate food, but on the host, who is his superior, and able to exalt and to destroy him (compare the cautious maxims in Ecclesiasticus 13:2, 6, 7, 11, etc.
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