Conversion in Judaism is an irrevocable process.
"...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 rather that he or she literally becomes the seed of the Avot and Imahot. For this to happen, a quasi-biological miracle is required. The Gentile needs to be reborn as a direct descendant of Avraham and Sara. This is accomplished by immersion in a mikva, clearly symbolizing the mother’s womb through which one is born. The proof for this far-reaching conclusion is the fact that, according to the Torah, a convert is technically allowed to marry his or her own mother, father, brother, or sister. This may sound 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 (re)born with no biological attachments except to Avraham and Sara. This speaks volumes. It is true that the rabbis forbade converts to marry their close relatives, fearing that people might claim the Gentile gave up a stricter religion for one with more lenient rules of morality.[2] But the fact that such marriages are rabbinically forbidden does not change the fact that they are biblically permitted."
(ט) יִשְׂרָאֵל מוּמָר שֶׁקִּדֵּשׁ, קִדּוּשָׁיו קִדּוּשִׁין גְּמוּרִים. וּצְרִיכָה מִמֶּנּוּ גֵּט. וַאֲפִלּוּ זַרְעוֹ שֶׁהוֹלִיד מִשֶׁהֵמִיר, אִם קִדֵּשׁ אוֹתוֹ זֶרַע יִשְׂרְאֵלִית, קִדּוּשָׁיו קִדּוּשִׁין. וְדַוְקָא שֶׁהוֹלִידוֹ מִיִּשְׂרְאֵלִית, אֲפִלּוּ מֻמֶרֶת. אֲבָל אִם הוֹלִידוֹ מִן הַגּוֹיָה, דִּינוֹ כְּגוֹי, אֲפִלּוּ הָיָה הַמּוֹלִיד יִשְׂרָאֵל שֶׁאֵינוֹ מוּמָר. אֲבָל יִשְׂרְאֵלִית מֻמֶרֶת שֶׁיֵּשׁ לָהּ זֶרַע עִם הַגּוֹי, שֶׁקִּדֵּשׁ, קִדּוּשָׁיו קִדּוּשִׁין (מָרְדְּכַי סוֹף הַחוֹלֵץ):
(9) If a Jewish apostate betrothed [a Jewish woman] his betrothal is completely valid, and she requires a writ of divorce. Even if he had children after he left Judaism, if one of those children were to betroth a Jewess, the betrothal is valid. This is only true if he had children with a Jewess, even if she is an apostate. If, however, he had children with a non-Jewess, the children are considered non-Jews, even if the father is a Jew who is not an apostate. Rem"a: If a Jewess apostate had a child with a non-Jew, that child's betrothal is valid.
Two differing philosophical views on the nature of giyur:
A) a person accepts the obligations and commandments and through that acceptance transforms into a Jew
B) a person joins the Jewish kinship and hence becomes obligated to all of the commandments
A) Jewishness as faith-based
B) Jewishness as ethnicity
Commitment generates Jewishness
the acceptance of Torah leads to a new spiritual identity of the convert and he or she assumes the identity of all the others who are likewise obligated.
Accepting the commandments is therfore considered "The very essence of conversion, so that if he did not accept upon himself Torah and commandments, it is as if he did not accept upon himself to become a Jew, and no conversion has taken place"
Jewishness as primarily joining a kinship. Conversion as form of biological rebirth.
This rebirth generates obligation to mitzvot.
וגר שנתגייר כקטן שנולד דמי:
And a convert who just converted is like a child just born.
תנו רבנן גר שבא להתגייר בזמן הזה אומרים לו מה ראית שבאת להתגייר אי אתה יודע שישראל בזמן הזה דוויים דחופים סחופים ומטורפין ויסורין באין עליהם אם אומר יודע אני ואיני כדאי מקבלין אותו מיד
ומודיעין אותו מקצת מצות קלות ומקצת מצות חמורות ומודיעין אותו עון לקט שכחה ופאה ומעשר עני ומודיעין אותו ענשן של מצות אומרים לו הוי יודע שעד שלא באת למדה זו אכלת חלב אי אתה ענוש כרת חללת שבת אי אתה ענוש סקילה ועכשיו אכלת חלב ענוש כרת חללת שבת ענוש סקילה
וכשם שמודיעין אותו ענשן של מצות כך מודיעין אותו מתן שכרן אומרים לו הוי יודע שהעולם הבא אינו עשוי אלא לצדיקים וישראל בזמן הזה אינם יכולים לקבל לא רוב טובה ולא רוב פורענות ואין מרבין עליו ואין מדקדקין עליו
קיבל מלין אותו מיד נשתיירו בו ציצין המעכבין את המילה חוזרים ומלין אותו שניה נתרפא מטבילין אותו מיד ושני ת"ח עומדים על גביו ומודיעין אותו מקצת מצות קלות ומקצת מצות חמורות טבל ועלה הרי הוא כישראל לכל דבריו
אשה נשים מושיבות אותה במים עד צוארה ושני ת"ח עומדים לה מבחוץ ומודיעין אותה מקצת מצות קלות ומקצת מצות חמורות
§ The Sages taught in a baraita: With regard to a potential convert who comes to a court in order to convert, at the present time, when the Jews are in exile, the judges of the court say to him: What did you see that motivated you to come to convert? Don’t you know that the Jewish people at the present time are anguished, suppressed, despised, and harassed, and hardships are frequently visited upon them? If he says: I know, and although I am unworthy of joining the Jewish people and sharing in their sorrow, I nevertheless desire to do so, then the court accepts him immediately to begin the conversion process.
And the judges of the court inform him of some of the lenient mitzvot and some of the stringent mitzvot, and they inform him of the sin of neglecting the mitzva to allow the poor to take gleanings, forgotten sheaves, and produce in the corner of one’s field, and about the poor man’s tithe. And they inform him of the punishment for transgressing the mitzvot, as follows: They say to him: Be aware that before you came to this status and converted, had you eaten forbidden fat, you would not be punished by karet, and had you profaned Shabbat, you would not be punished by stoning, since these prohibitions do not apply to gentiles. But now, once converted, if you have eaten forbidden fat you are punished by karet, and if you have profaned Shabbat, you are punished by stoning.
And just as they inform him about the punishment for transgressing the mitzvot, so too, they inform him about the reward granted for fulfilling them. They say to him: Be aware that the World-to-Come is made only for the righteous, and if you observe the mitzvot you will merit it, and be aware that the Jewish people, at the present time, are unable to receive their full reward in this world; they are not able to receive either an abundance of good nor an abundance of calamities, since the primary place for reward and punishment is in the World-to-Come. And they do not overwhelm him with threats, and they are not exacting with him about the details of the mitzvot.
If he accepts upon himself all of these ramifications, then they circumcise him immediately. If there still remain on him shreds of flesh from the foreskin that invalidate the circumcision, they circumcise him again a second time to remove them. When he is healed from the circumcision, they immerse him immediately, and two Torah scholars stand over him at the time of his immersion and inform him of some of the lenient mitzvot and some of the stringent mitzvot. Once he has immersed and emerged, he is like a born Jew in every sense.
For the immersion of a woman: Women appointed by the court seat her in the water of the ritual bath up to her neck, and two Torah scholars stand outside the bath house so as not to compromise her modesty, and from there they inform her of some of the lenient mitzvot and some of the stringent mitzvot.
(יז) גֵּר שֶׁלֹּא בָּדְקוּ אַחֲרָיו אוֹ שֶׁלֹּא הוֹדִיעוּהוּ הַמִּצְוֹת וְעָנְשָׁן וּמָל וְטָבַל בִּפְנֵי שְׁלֹשָׁה הֶדְיוֹטוֹת הֲרֵי זֶה גֵּר. אֲפִלּוּ נוֹדַע שֶׁבִּשְׁבִיל דָּבָר הוּא מִתְגַּיֵּר הוֹאִיל וּמָל וְטָבַל יָצָא מִכְּלַל הָעַכּוּ''ם וְחוֹשְׁשִׁין לוֹ עַד שֶׁיִּתְבָּאֵר צִדְקוּתוֹ. וַאֲפִלּוּ חָזַר וְעָבַד עֲבוֹדָה זָרָה הֲרֵי הוּא כְּיִשְׂרָאֵל מוּמָר שֶׁקִּדּוּשָׁיו קִדּוּשִׁין. וּמִצְוָה לְהַחֲזִיר אֲבֵדָתוֹ מֵאַחַר שֶׁטָּבַל נַעֲשָׂה כְּיִשְׂרָאֵל. וּלְפִיכָךְ קִיְּמוּ שִׁמְשׁוֹן וּשְׁלֹמֹה נְשׁוֹתֵיהֶן וְאַף עַל פִּי שֶׁנִּגְלָה סוֹדָן:
A proselyte who ... was circumcised and immersed in the presenceof three laymen is a proselyte. Even if it is known that heconverted for some ulterior motive, once he has been circumcised and immersed he has left the status of a non-Jew... even if he recanted, and worshipped idols, he is a Jewish apostate; if he betroths a Jewish woman according to halakhic procedure - they are betrothed; and an article he lost must be returned to him as to any other Jew. Having immersed, he is a Jew.
ומודיעין אותו מקצת מצות - דהשתא ע"י טבילה הוא נכנס לכלל גירות הלכך בשעת טבילת מצוה צריך לקבל עליו עול מצות:
...and inform him on some of the commandments: it is precisely through immersion that enters into the status of conversion, therefore at the moment of immersion he needs to obligate himself to receive the yoke of the commandments.
מי לא טבלה לנדותה - תימה דאמר לקמן (דף מו:) דגר צריך שלשה דמשפט ... וי"ל האי דבעינן שלשה היינו לקבלת המצות...
...A convert needs three to judge... and there are those who say that three are needed for kabbalat mitzvot (the acceptance of the commandments).
If we say we "accept something" does that mean that we are informed about each and every little detail? Or does it mean we accept "the large picture"?
And does accept mean to accept it as theoretical knowledge or does it mean to accept it as a standard of practice?
The convert must become a follower of Avraham’s and Sara’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. He or she must somehow embrace the great institutions of Judaism such as Shabbat, kashrut, and sexual dignity. Striving for kedusha / holiness and tahara / spiritual purity is of primary importance.
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 kabbalat mitzvot (acceptance of the commandments) is sufficient. Anything less will not do. Others maintain that a sincere desire to be a part of the Jewish people is sufficient, though not ideal.