Is talmud torah a shemirah just when the person is actually learning the torah or even after he is now longer learning and he is now doing something else?
Ari
Shalom Ari,
Thank you for your question on an extremely important topic!
Rav Yosef and Rava in Sotah 21a set the map. Rav Yosef holds that a Mitzvah is Maginah even after one stops doing it, while Torah is both Maginah u'Matzilah even when one is no longer learning. Rava challenges this from Doeg and Achitofel and concludes that Torah is Maginah u'Matzilah only while learning. After stopping, it remains Maginah but not Matzilah.
What are these two elements? Rashi (Sotah 21a) defines Maginah as bodily protection from Yisurim, and Matzilah as spiritual rescue from the Yetzer not to fall into Aveirah. The Maharsha elaborates that Maginah is from Yisurim, not from Misah (see also Sanhedrin 69b and 106b), which weakens the proof from early death. The Vilna Ga'on (on Mishlei 31:12) reads Rava's attack as aimed at the Matzilah dimension, that Torah did not save them from sin, leaving room that Maginah can still persist after learning; a similar line is cited by Rav Yosef Shalom Elyashiv zt'l in the name of the Tosfos Shantz. The Or ha'Chayim (Bamidbar 13:26) notes Chazal's conclusions that such Torah might have been she'Lo Lishmah or preceded by entrenched sin (compare Chagigah 15b), thus weakening its protection. The Chida (Pesach Einayim to Sanhedrin 102a) adds that Torah that guards from Ma'aseh Aveirah more than from Machshavah explains remaining difficulties (e.g., Yeravam ben Nevat).
For practice, Kesubos 77b is key: Rebbi Yehoshua ben Levi relied on Torah's Shemirah when joining the sick, but Rebbi Yochanan, Rebbi Zeira, Rebbi Elazar, Rebbi Ami, and Rebbi Asi did not. Rashi there implies Rebbi Yehoshua ben Levi relied on it specifically while learning; the Ritva and later authorities stress his exceptional Kedushah, Taharah, and Zechuyos. The Hafla'ah (Kesubos 77b) writes that his powerful Emunah removed fear; the Beis David (Leiter, Siman 22) notes "Nafish Zechusei Tovah"; Rav Shlomo Zalman Auerbach zt'l (Halichos Shlomo, Tefilah, p. 97) and Rav Elyashiv zt'l both caution that for us, whose Torah is not fully Lishmah, we must not rely on this Shemirah. More broadly, Shabbos 32a warns never to enter danger and depend on a miracle, and Berachos 61b shows Rebbi Akiva's Mesirus Nefesh to teach Torah was a Sha'as ha'Shmad, not a general license to ignore risk.
I hope this helps!
Aharon Steiner