The Talmud derives the laws of giyur from the story of Ruth and Naomi, teaching that a potential convert is informed of both the hardships and privileges of joining Israel; Ruth's acceptance becomes the halachic template for sincere conversion connected to Torah acceptance.
תָּנוּ רַבָּנַן: גֵּר שֶׁבָּא לְהִתְגַּיֵּיר בִּזְמַן הַזֶּה, אוֹמְרִים לוֹ: מָה רָאִיתָ שֶׁבָּאתָ לְהִתְגַּיֵּיר? אִי אַתָּה יוֹדֵעַ שֶׁיִּשְׂרָאֵל בִּזְמַן הַזֶּה דְּווּיִים, דְּחוּפִים, סְחוּפִים וּמְטוֹרָפִין, וְיִסּוּרִין בָּאִין עֲלֵיהֶם? אִם אוֹמֵר: יוֹדֵעַ אֲנִי, וְאֵינִי כְּדַאי — מְקַבְּלִין אוֹתוֹ מִיָּד. וּמוֹדִיעִין אוֹתוֹ מִקְצָת מִצְוֹת קַלּוֹת וּמִקְצָת מִצְוֹת חֲמוּרוֹת, וּמוֹדִיעִין אוֹתוֹ עֲוֹן לֶקֶט שִׁכְחָה וּפֵאָה וּמַעְשַׂר עָנִי. וּמוֹדִיעִין אוֹתוֹ עׇנְשָׁן שֶׁל מִצְוֹת. אוֹמְרִים לוֹ: הֱוֵי יוֹדֵעַ שֶׁעַד שֶׁלֹּא בָּאתָ לְמִדָּה זוֹ, אָכַלְתָּ חֵלֶב — אִי אַתָּה עָנוּשׁ כָּרֵת. חִלַּלְתָּ שַׁבָּת — אִי אַתָּה עָנוּשׁ סְקִילָה. וְעַכְשָׁיו, אָכַלְתָּ חֵלֶב — עָנוּשׁ כָּרֵת, חִלַּלְתָּ שַׁבָּת — עָנוּשׁ סְקִילָה. וּכְשֵׁם שֶׁמּוֹדִיעִין אוֹתוֹ עׇנְשָׁן שֶׁל מִצְוֹת, כָּךְ מוֹדִיעִין אוֹתוֹ מַתַּן שְׂכָרָן. אוֹמְרִים לוֹ: הֱוֵי יוֹדֵעַ שֶׁהָעוֹלָם הַבָּא אֵינוֹ עָשׂוּי אֶלָּא לְצַדִּיקִים, וְיִשְׂרָאֵל בִּזְמַן הַזֶּה אֵינָם יְכוֹלִים לְקַבֵּל
§ 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;