On the one hand:
Torah study protects forever, in this life, in death, and in the resurrection of the dead. (Sotah 5b, paraphrased)
Rabbi Shimon Ben Lakish said: Troubles are removed from all those who study Torah. (Berachot 5a)
On the other hand:
"Because he despised the word of the Lord and has breached His commandment, that soul shall be excised [hikkaret tikkaret]; his iniquity shall be upon him"... “hikkaret”, cut off in this world, “tikkaret”, cut off in the World-to-Come... Rabbi Nehorai says: This is about anyone who could engage in Torah but who did not engage. (Sanhedrin 99a, which is codified in Halacha in Mishna Torah and the Shulchan Aruch)
“He who commits adultery with a woman lacks understanding,” Reish Lakish says: This is one who studies Torah intermittently, as stated [on the subject of Torah] “For it is a pleasant thing if you keep them within your belly; let them be established on your lips.” (Sanhedrin 99b)
The Holy One forgave Israel even for Avodah Zara and murder, but for neglecting Torah study Hashem never forgave them. (Yerushalmi Chagigah 1:6)
How should one reconcile these different Talmud quotes? It seems to be that the first two quotes sound as though even a little Torah will go a long way, but the next three seem all or nothing, and if you waste time once in a blue moon it could all be thrown away! Please help me in my endeavor to understand the Talmud and have a Torah-based viewpoint on the mitzvah of learning Torah.
Additionally, this is not my main question but a related aside, Chagigah 9a says, "'A twisted thing cannot be corrected.' Rabbi Shimon Bar Yochai says this refers to a Torah Sage who separated himself from the Torah," but Chagigah 15b says "A Torah scholar, even if he sinned [lit: was soured], his Torah does not become repulsive," referring to Achar, and if anyone is one who "separated himself from the Torah," it would be he!