The Term “Haftara”
1. Finishing Shacharis. We find multiple reasons and sources for the word “haftara” as the term for laining from Navi on Shabbos; we will mention a few. Some say it means finishing, as in “אין מפטירין אחר הפסח אפיקומן,” as it finishes Shacharis (אבודרהם, סדר שחרית של שבת).
2. “Patur.” Others explain it is related to the word “patur,” i.e., with this laining, the members of the tzibbur exempt themselves and finish their chiyuv to lain (מחזור ויטרי).
Reasons for the Institution of the Haftara
3. In place of Kriyas HaTorah. Some explain the reason as follows: part of the decree against the Jews practicing religion [in the time of the wicked Antiochus, king of Yavan (תשו' רבי אליהו בחור, ערך פטר)] was that they were forbidden from reading the Torah. To parallel the seven aliyos, each with a minimum of three pesukim, Chazal instituted the laining of 21 pesukim from Navi (אבודרהם שם). Even after the decree was annulled, the minhag remained (שם, לבוש, ב''ח, ט''ז, מ''ב).
4. To learn Navi. An additional reason given is that people back then remained in shul for an hour after davening, even during the week, and they would bring sefarim and learn Torah, Navi, Mishna, and other teachings. When poverty spread, people were preoccupied with work during the week and were unable to learn as much Torah. They continued learning Torah but stopped learning Navi. On Shabbos and Yom Tov, when melacha is assur and people were free, they resumed their original practice of reading Torah and concluding with a section of Navi related to the topic of the day (שבלי הלקט בשם רש''י הובא בב''י סי' קל''ב).
5. Honor for the Nevi’im. Some write haftara was instituted for the honor of the Nevi’im (תשב''ץ ח''א סי' קל''א), and it dates back to the time of Ezra (ס' המכריע לתוס' רי''ד סי' ל''א).
6. It should be noted that although we lain from Navi, we do not finish all the Nevi’im through all the yearly haftaros as we do for the Torah. We only lain a fraction of them, with the majority of haftaros coming from Yeshaya, Trei Asar, and Melachim.