As Benjamin begins, he sets up a stylistic theme for the way he will construct the argument he will present. He uses a contradiction that begins with what he has not done, and then emphasizes what he has done. The introduction confirms the importance of this occasion by saying that he did not command them to come and trifle with his words, but that they would understand them, implying that they would have something to do as a result.
This should suggest that this is a different occasion. The people have gathered in what appears to have been a ritual occasion, perhaps the Feast of Tabernacles. It is possible that there would have been some traditional speech by the king, and perhaps it might have been the kind of speech that Jacob’s people had come to hear on the occasion when he also had to tell them that they would not hear those pleasing words.
The signal of the opening is that this was not a common ritual with standard blessings. Something different was coming. That difference begins with the “this is what it is not, this is what it is” type of introduction. That method of setting the scene continues as Benjamin sets his scene.