Shavuos 14 - 20
Torah as Preventive Medicine
Rabbi Yehoshua ben Levi recited Psalm 91 of Tehillim before retiring at night to protect himself against the dangers of the night. (This has been universally accepted as part of the Shma recited before going to sleep.) In response to the challenge that it is forbidden to conjure healing with words of Torah the Talmud explains that what the sage did was preventive rather than curative.
This distinction is utilized by Maharsha in explaining the counsel given by this same sage (Eruvin 54a) that "one who feels an ache in his head should study Torah." The subject there is not one who already suffers a serious ailment in his head, only a slight ache which causes him to be concerned that it will develop into full fledged illness. His study of Torah is therefore of a preventive nature which is not only permitted but advisable.
- Shavuos 15a
The Beis Hamikdash, states the Sage Abaye, cannot be constructed at night. When the Torah describes the erection of the first Sanctuary in the wilderness it speaks of "the day the Mishkan was established" to teach us that such construction cannot take place at night.
This raises a problem regarding a scenario presented by the Talmud (Sukkah 41a) of the Third Beis Hamikdash being constructed on the night between the 15th and 16th of Nissan and the implications of such a situation for the post-Beis Hamikdash decree of Rabbi Yochanan ben Zakkai to refrain from eating new grain until the entire 16th day has passed.
The ban on nocturnal construction, explains Rashi (ibid.), applies to human effort. The Beis Hamikdash of the future, to which we are looking forward, will descend from Heaven completely built as we say in the Shirah which the Children of Israel sang at Yam Suf "the Mikdash which Your hands formed, Hashem" (Shmos 15:17).
- Shavuos 15b