A Jewish congregation was arguing over whether one should stand or sit during the Kaddish prayer. Half of the congregation said one should sit, while the other half insisted one should stand. Every time the Kaddish was recited they shouted at each other, “Sit down!” “Stand up!” The fighting became so bad that the congregation was split in two, each half contending that they knew the proper tradition.
Finally, the rabbi decided to visit a one-hundred-year old member of the synagogue who was living in a nursing home. He took a delegation from each of the arguing sides with him to see the oldest member of the “shul”. “Now, tell us,” said the rabbi, “what is our tradition?” “Should we stand during the Kaddish?” “No,” said the old man. “That is not our tradition.” “Well, then,” said the rabbi, “should we sit during the Kaddish?” “No,” the old man, “that is not our tradition.” “But we need to know what to do,” said the rabbi, “because our congregation members are fighting non-stop over this. “That,” said the oldest member of the congregation, “that is our tradition.”
“This may you eat of all that is in the waters: Everything that has fins and scales, may you eat. But anything that has no fins and scales, you may not eat,” The Torah states in this week’s portion of Reah. 
The Mishna states an interesting fact:  "All [fish] that have scales also have fins [and are thus kosher]; there are [fish] that have fins but do not have scales [and are thus unkosher]."
This raises the big question, as the Talmud itself wonders:  Why are fins presented as an identifying sign for kosher fish when they are redundant, since scaled fish inevitably have fins? The Torah could have given only scales as an identifying kosher sign, and that would have automatically included fins?
The Talmud’s answer consists of three words: “Yagdil Torah Veyaadir,” to make the Torah larger and bigger. In order to enhance the Torah, it adds the kosher sign of fins.
This answer seems strange. How does the unnecessary sign of fins make the Torah larger and greater? Does this single extra word “fins” really add something significant to the Torah? Besides, the Five Books of Moses are well known for their conciseness, and the Talmud often searches for the reason behind a seemingly superfluous word. Why can’t the Talmud simply state, “Yagdil Torah Veyaadir,” to make the Torah larger and greater, as it does in this case?
Journey of a Nation
Here we discover, once again, how a single extra word in the Torah (“fins”) and a single thought in the Talmud, reflects a millennia-long saga and captures a timeless lesson for the Jewish narrative.
The Talmud relates  how the second century great Talmudic sage Rabbi Akiva taught Torah to the masses at a time when the Roman government, under the Emperor Hadrian, prohibited such activity with the threat of death. Another sage, Pappus ben Judah, warned Rabbi Akiva that he was endangering his life. Rabbi Akiva replied with the following parable:
A fox was once walking by the bank of a river, and saw fish darting from place to place. "What are you fleeing from?" he asked the fish. "To escape the nets of the fisherman" the fish replied. "In that case," said the fox, "come and live on dry land together with me." "Are you the one they describe as the cleverest of animals?" the fish asked the fox. "You are not clever but foolish. If we are in danger here in the water where we live, how much more so would we be in danger on dry land, where we would surely die.”
Torah is to Jewish survival, said Rabbi Akiva, as water is to fish. Yes, we are in danger, but if we were to leave Torah, which sustains our existence, to enter the dry land of the Romans, we would certainly perish.
The long, complex and extraordinary journey of the Jewish people throughout history is thus compared to the life of a fish in water. Our survival and success in the waters requires two components: we must have scales, but we must also have fins.
Armor and Progress
The scales are a thickened layer of "skin" that is designed to protect the fish, to ward off external dangers, such as sudden changes in temperature and water pressure or other attacking fish. Scales are the “armor” protecting the body of the fish.
Fins, the wing-like organs that propel fish forward, allow the fish to move along in the water, to make progress and advance to great distances, to journey in different directions, and not to remain in one space and location.
For thousands of years Jews have been arguing about many issues. But if you want to sum up the quintessential Jewish debate, you might say that it is the dispute between Rabbi Scales and Dr. Fins. In today’s Jewish geography, Rabbi Scales might be residing in Boro Park or Jerusalem, and Dr. Fins in Greenwich or Tel Aviv.
Remain in the Orbit of Judaism
Rabbi Scales’ argument is simple. To endure the trials and tribulations of thousands of years of exile and all forms of persecution, we must develop “scales,” a "thick skin" to shield us from dangerous external influences. We managed to survive because of our ability to resist change and to limit our interaction with the outside world.
“Modernity,” our esteemed Rabbi Scales argues, “is the enemy. Progress is dangerous. The walls of the ghetto may have come tumbling down, but we will rebuild them, if not physically, at least socially. Let us remain behind our ‘armor,’ let us dwell in our cocoon, and then we will be kosher and pure. We will survive and thrive.
“’If it was good for our grandparents it is good for us’—that is my motto,” declares Rabbi Scales. We will continue doing the same things Jews have been doing for three thousand years: Wrap Tefillin each morning, keep Shabbos, pray, study Torah, give our children a thorough Jewish education, keep kosher, use the Mikvah, etc. This will secure our future.
Leave the Shtetl
In contrast, we have our prominent Dr. Fins, a graduate from an Ivy League University and a man of the world. “Rabbi Scales, with all due respect, it is time to use your fins and swim to the other side of the Atlantic. You are not living in the shtetl any longer; we have at last crossed the ocean. We must advance with the times, and become part of the modern conversation. Our key to success is “fins,” the flip-flap wings which help us advance with history, to become progressive, to join the larger culture.
“If we want remain relevant and fresh,” argues Dr. Fins, “we must integrate rather than isolate; we ought to become players within the world arena.”
The two Jews never stop arguing, even if they rarely meet each other. Fins continues to accuse Scales of being an isolationist, a fanatic, an old fashion fundamentalist; Scales accuses Dr. Fins of being an ambivalent, feeble, self-denigrating, and assimilated Jew.
As it turns out, none of these voices capture the full calling of Judaism, as we shall see.
The Key to Survival
Comes the Mishna and states this fact: All [fish] that have scales also have fins [and are thus kosher]; there are [fish] that have fins but do not have scales [and are thus unkosher]." What does this represent symbolically?
As Rabbi Akiva understood so well, even if our nation was to develop the most effective fins, a most canny ability to integrate into the larger society, it will not necessarily produce scales—the armor we need to ensure our continuity and retain our identity. Assimilation is natural and inevitable. For the Jewish people to survive there is only one way: through our millennia-long “scales,” our Torah and Mitzvos. Why?
When a scientist seeks to discover the essential properties of an element of nature, he must undertake a series of experiments under the most varied conditions to discover those properties which are alike under all conditions.
The same principle should be applied to Jewish survival. We have been around for over three-thousand years. In the course of this time, Jews have lived under extremely varied conditions. They were dispersed across the world; they had multiple languages and absorbed an assortment of cultures. Is there any single “property” common to all of Jewish history? Is there one phenomenon that pervades all of Jewish history to which we can attribute our survival?
It is not its land, language, or culture—these have varied from age to age and from place to place. The only constant single factor that has linked the Jewish people across space and time from Sinai to the present was the Torah and its Mitzvos. It is through the Torah way of life that the key to our eternity lies. We must secure our scales if we wish to survive. Fins alone will not do the trick.
Conversely, if we develop scales, if we remain tenaciously connected to our spiritual heritage, to the study of Torah and the observance of its Mitzvos, then we will have “fins” too, we will possess the ability to advance and grow with the times and make a true impact on the world as well. The more entrenched we are in our Judaism—the deeper and broader our universal impact will reach. It’s like with love: the more you love your wife and children, the more you can love other human beings outside of your family.
Saturating the World
If so, asks the Talmud, why was it necessary to give the sign of “fins” at all? Would it not suffice to define “scales” as the exclusive identifying kosher sign of fish? To define the question in the above context: to be a “kosher” Jew and to ensure the “kosher” status of the Jewish people, it seems, all you need are scales. Why then does the Torah also add fins as an identifying kosher sign?
The answer is: Yagdil Torah Veyaadir, to make the Torah larger and greater. For a fish to be kosher, for the Jewish people, compared to the fish, to fulfill their mission in life, it must have scales, but they must also have fins. And the latter is also essential to the kashrus of the fish. Because Our mission in life is not only to maintain our own spiritual and moral integrity and to shield ourselves from the negative influences of the world; our role is also to saturate the entire world with the light of Torah; to transform the entire universe into an abode for G-d. It is not enough for us to remain protected behind our scared armor. Rather, we must acquire fins, and broaden our sphere of influence to the furthest possible places, and each of us has a sphere of influence—our family, community, business associations, and all other contacts.
The truth, the depth, the light of Torah must permeate all of the Jewish people, and all of humanity. We must swim and engage the world not because of insecurity, but because the whole world craves and yearns for the inspiration and guidance of Torah, because every person deserves to discover the G-dliness within his or her heart.  Deep down, all of humanity yearns to declare “yisgadal veyiskadash shemei rabah!” 
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 Deuteronomy 14:9-10
 Nidah 51b
 Nidah ibid; Chulin 66b
 Berachos 61b
 This may be the reason why Jacob used the metaphor of fish when he blessed the sons of Joseph on his deathbed: "May He bless the lads, and let them carry my name, along with the names of my fathers, Abraham and Isaac. May they increase in the land like fish.” (Genesis 48:16)
Unlike all of their cousins, Joseph’s sons were the first Jewish children to be born and bred in exile. They were the first generations of Jews to grow up in an environment completely alien to Judaism. More than any of Jacob's other grandsons they needed the blessing of “fins and scales.”
 This essay is based partially on Reshimos vol. 39 and other sources.