Mystery surrounds the source of a familiar custom. The gemara tells us that on the very last day of Succot (known as "Simchat Torah") we read the last parsha of the Torah - "Beracha" - and for the haftarah we read from the eighth chapter of Melachim I (8:22) about King Solomon's prayer at the inauguration of the Beit Hamikdash.

Rabbeinu Nissim (Ran) explains the choice of these two sections. Simchat Torah is the climax of the festivals, and it is fitting to read on that day the blessings which Moshe gave to all of Israel. Since a haftarah must follow the spirit of the Torah reading, it is fitting that Moshe's blessings be followed by the blessings Solomon gave to all of his people.

Tosefot already calls attention to the custom - which is the one we follow - to read as the haftarah the first chapter of Yehoshua. Rabbeinu Nissim's explanation of this custom is that since we concluded our Torah reading with Moshe's passing, it is fitting that the haftarah consist of what Hashem commanded Moshe's disciple, Yehoshua, immediately afterwards.

The explanations are perfect. But there is a mystery as to why we have abandoned what the gemara determines as the haftarah. Tosefot cites a source that says the Gaon Rav Hai instituted this custom, but Tosefot wonders what reason there was for deviating from what our gemara says.

Rabbeinu Asher (Rosh) cites the Jerusalem Talmud as the source for this custom, but Korban Netanel comments that he was unable to find it there.

Whatever the source, this is the universal Jewish custom just as is the celebration which surrounds the completion of the reading of the entire Torah. The source for this celebration, however, is no mystery. The Midrash, referring to King Solomon making a festive banquet for all his servants when he realized that Heaven had granted his request for wisdom (Melachim I 3:15), declares this as a source for celebrating when we finish reading the entire Torah.

Just as Solomon felt a need to celebrate the gift of wisdom granted by Heaven, so do all Jews, who feel so much wiser as a result of reading the entire Torah for a year, feel the need to celebrate with Simchat Torah.

• Megillah 31a