It is for this very reason that we find the mitzvah of relating the story of our exodus in the plague of locusts. For even without being commanded to have a Seder night of relating to our children and grandchildren the story of our exodus, we would have naturally done it anyway. We are so full of gratitude not only for our exodus and freedom, but we are extremely thankful for becoming the chosen nation and receiving the Torah which only came about because of our exodus. Irrelevant of the command to do so, every anniversary of Pesach on our own accord we would have celebrated with a family gathering. This  is the reason why a beracha prior to our beginning the mitzvah of telling the story of our exodus was not instituted. Our chachamim desired that the story should take the nature of natural gratitude and thank you that stems from individuals who feel a deep hakaras hatov to their benefactor.

With this we can understand another point that the Ari says: the gematriah ofארבה is יצחק. This is reinforced by the passuk (Yehoshua 24,3)וארבה את זרעו ואתן לו את יצחק . The connection is that Yitzchak Avinu was known to have perfected the middah of din and fear of Hashem. I once met a chasid from the Kalever Rebbi shlita of Williamsburg and as we were discussing his relationship to the Rebbi he said a line that I will never forget and I tell it over to my bachurim all the time “I don’t make a move  without the Rebbe”. This statement personifies the middah of true emunah and yiras shamayim. One who possesses such a middah doesn’t really have to speak to the Rebbe at every little juncture of bechirah and move but rather he must ask himself what  would the Rebbe have advised me to do in this situation. What comes out is that without receiving any orders for one’s particular situation one intuitively knows what to do. Yitzchak for example was never commanded to be a karban at the Akaidah. It was only Avraham who was told my Hashem to take his son and shecht him. Yet Yitzchak intuitively knew that this was the right thing to do without even being commanded to do so. Therefore, it is Yitzchak whose life personifies a conduct that parallels the species of the locusts.