"Three signs are there for this nation: they are rachmanim, merciful; bayshanim, have a sense of shame; and gomlei chasadim, perform acts of kindness" (Yevamot 89a). The distinguishing mark of the Jewish people is not our observance of Shabbat, kashrut, and a host of other mitzvoth. Important as they may be, they are reflections of the values that are (or at least should be) the true hallmark of the Jew: mercy, shame, and kindness.
One of the key distinctions between the land of Israel and the Diaspora is the ability to observe the many mitzvot between man and the land. The seventh chapter of Yevamot focuses on the intricacies of the laws of terumah, which may be eaten only by a kohen or a member of his household. The chapter begins by analyzing the case of a kohen marrying someone prohibited to him, such as a divorcee.
"The signature of G-d is truth" (Sanhedrin 64a). "Accept the truth from wherever it comes" (Rambam, Introduction to Avot). There are few values more important than that of truth. While Jewish law allows and encourages one to tell a white lie for the sake of peace (Yevamot 65b), such has its limits.
"And G-d blessed them; and G-d said unto them: 'Be fruitful, and multiply, and replenish the earth, and subdue it; and have dominion over the fish of the sea, and over the fowl of the air, and over every beast that walks on the land'" (Breisheet 1:28). Here we have the source for the very first mitzvah of the Torah--or do we?
“Rav ordered that lashes be given to any person who betrothed by cohabitation, who betrothed in the open street, or who betrothed without previous negotiation; who annulled a letter of divorce, or who made a declaration against a letter of divorce; who was insolent towards the representative of the rabbis, or who allowed a rabbinical ban upon him to remain for thirty days and did not come to the Beit Din to request the removal of that ban; and of a son-in-law who lives in his father-in-law's house” (Yevamot 52a).
Masechet Kiddushin opens by delineating the three methods by which one is mekadesh, betroths, a woman. Masechet Yevamot, on the other hand, opens by delineating the fifteen cases where yibum is not required and hence not allowed. The first fifty pages of the masechet focus on analyzing various scenarios and their impact on the mitzvah of yibum. Only after we near the midway point of the masechet does the Gemara actually discuss the process of yibum.
"Shimon ben Azzai said: I found a scroll of genealogy, and it was written, 'So-and-so is a mamzer, [having been born] from [a forbidden union with] a married woman; and it was written, 'the teaching of Rabbi Eliezer ben Jacob is small in quantity, and clean'. And in it was also written, 'Menashe slew Isaiah'" (Yevamot 49b).
"A convert who comes to convert bizman hazeh, nowadays...we inform him of the importance of leket, shichichah, peah and ma'aser ani" (Yevamot 47a). The Gemara lists only six specific mitzvoth we must teach a convert. There is no surprise that this list includes Shabbat and kashrut--probably the two most distinguishing aspects of being a Jew, sanctifying as they do our time and our bodies.