In addition to ordaining the reading of the parsha on Shabbat morning, Ezra the Scribe also instituted that the Torah be read at Minĥa. Three people are called up at Minĥa and the beginning of the next parsha is read. This section is read on Monday and Thursday mornings as well, in preparation for and introduction to the next week’s reading.
The Sages state that this ordinance was on account of “yoshvei keranot” (idlers; lit. “those who sit on corners”) (BK 82a). Some explain this term to refer to merchants and artisans who sat in their stores and did not attend Shaĥarit services during the week. Since they did not hear the Torah reading of Monday and Thursday mornings, they would have been unprepared for the upcoming parsha. To ensure that they would hear the introductory reading at least once, Ezra instituted that it be read at Minĥa on Shabbat, when everyone is able to attend (Rashi; Rosh).
Others explain that Ezra was worried that people would get drunk at Shabbat lunch, and then they would be in no state to learn Torah. Ezra therefore instituted that there be a Torah reading at Minĥa so that out of respect for the reading everyone would congregate in the synagogue. Thus they would neither get drunk nor waste time. Along the same lines, King David said to God: “Master of the Universe, this nation is not like other nations. When other nations have a festive meal they drink and get drunk and act silly. We are not like this, however. Although we eat and drink, we come to pray, as is stated: ‘As for me, may my prayer come to You, O Lord, at a favorable moment; O God, in Your abundant faithfulness, answer me with Your sure deliverance’” (Tehilim 69:14). This is why we recite this verse before reading the Torah at Minĥa (Shibolei Ha-leket).