As the State of Israel and its rabbinical courts head toward a large-scale showdown concerning conversion, it is remarkable that not one of the participants, including the Orthodox, has considered this major, crucial question: Is conversion at all possible? This may sound like a rhetorical question since the answer is in the affirmative. Yet, logically speaking, conversion to Judaism should not be possible. Just as it is impossible for a Jew whose father is not a Kohen to become a Kohen, similarly, it should be out of the question for a gentile to become a Jew. Either one is born into a family of Kohanim, or one is not. Presumably, then, either one is born a Jew, or one is not. Yet, conversion to Judaism is possible. How? Michael Wyshogrod, in his book The Body of Faith, gives an authoritative answer to this question: by means of a miracle. A gentile who converts to Judaism miraculously becomes part of the people of Israel. Unlike with Christianity, this does not just mean that the gentile now shares the beliefs of Judaism, but that he or she literally becomes the seed of the patriarchs and matriarchs. For this to happen, a quasi-biological miracle is required. The gentile needs to be reborn as a direct descendant of Abraham and Sarah. This is accomplished by immersion in a mikve (ritual bath), clearly symbolizing the mother's womb through which one is born. The proof of this far-reaching conclusion is that, according to the Torah, a convert is allowed to marry his or her own mother, father, brother or sister. This may sound sinister - even immoral - but for the profound, reflective thinker it is most telling and meaningful. The Torah views a convert as a completely new human being, recently born, with no biological attachments except for Abraham and Sarah. This speaks volumes. Though the rabbis forbade a convert to marry his or her mother or father, etc., fearing that it may look like sanctioning immorality (Yebamot 22a), it does not change the fact that they are biblically permitted to do so. THIS IS radically different from baptism in Christianity. After baptism, the prohibition of incest is not waived. The biological relationship between parents and the baptized person continues as before. Not so in Judaism. What is required is the total rebirth of a person, as if new. While Jewish law requires full respect for one's biological, non-Jewish parents, it simultaneously makes it clear that conversion is an extreme step with radical consequences. That Judaism is prepared to make this step, against all logic, so as to allow a non-Jew to become, literally, a child of Abraham and Sarah, shows it to be one of the most daring religions. No non-Jew should be denied the possibility of joining our nation, when there is a sincere desire to do so. It is, for this reason, impossible to argue that mere immersion in a mikve is sufficient. It is crucial that the potential convert desire to become a different person and undergo a deeply spiritual transformation. Human beings are not just a mass of plasma, complicated robots, or tool-making animals who can change their fundamental selves simply by immersing in a well of water. They are souls, with deep emotions. Conversion should be a well thought-out decision, rooted in the deepest recesses of the human soul. While this clearly includes the desire to become a part of the Jewish people, it is not enough. There is much more at stake. The convert must become a follower of Abraham's and Sarah's great legacy. This includes the acceptance of the oneness of God, the need to be righteous and the desire to inspire the world with the great moral foundations which were later solidified at Sinai, including Shabbat, kashrut, the longing for kedusha (holiness) and tahara (spiritual purity). Whether or not the convert must a priori take on all the commandments, or only some, is a matter of great debate among the authorities. There are some who maintain that only a full kabalat hamitzvot (taking on of the commandments) is acceptable. Others maintain that a sincere desire to be part of the Jewish people is sufficient, though not ideal. WHY THIS difference of opinion about such a crucial and far-reaching issue? Judaism and the Jewish people are intertwined, and interact in ways which nobody can fully grasp. Are we a religion, or a nation? If we are a religion, how can it be that somebody who does not believe in God or refuses to observe even one commandment still remains Jewish as long as he or she is born to a Jewish mother? And if we are a nation, why does religion determine who belongs and who does not? Any attempt to find a solution to this problem will always fail. There is no way to nail down these definitions. They elude us, and we must admit that we are confronted by one of the greatest mysteries of Jewishness. We become aware of the existence of something we cannot penetrate. It is for this reason our authorities have different views on the question of conversion. Is one converting mainly to a religion, mostly joining a nation, or some paradoxical combination of the two? Still, without a strong, religious component, conversion is a farce, just as it would be completely ridiculous to claim, conversely, that even though somebody is totally committed to the Torah, lives in its spirit, and has immersed in a mikve, he or she would not be considered part of the Jewish people. He or she is, but we do not really know why or how. We need both components, religion and nationhood, but cannot figure out how they relate to each other. WHILE CAUGHT in this strange mystery, however, we should neither make the mistake of thinking that only living by the laws of the Torah and being part of the Jewish people is what is ideally required. There is something called "Jewishness" or a Jewish neshama. Again, were we to try and define these, we may find ourselves accused of racial discrimination. Still, we all know that it is there. To be Jewish is to live in a spiritual order which cannot be narrowed down to doctrines, dogmas or commandments. Halacha and beliefs are not enough. Somehow, the convert must inherit the great spirit from Abraham and Sarah, which is more than the sum of all of the above parts but also different from all the above. What it really is and how it transpires we really do not know. But it is. So we can only ask that the convert accept all of this and initiate the climb up the ladder of observance, slowly but surely, combining nationhood with spiritual nobility. It sounds paradoxical? Well, it is. And let it be. It has served us well through thousands of years, and made us into an eternal and indestructible nation. Let us not take it lightly. The writer, founder and dean of the David Cardozo Academy in Jerusalem, is the author of many books, his latest being For the Love of Israel and The Jewish People (Urim).