About this future time our Sages said, ‘He who blackens his face learning Torah in this world, Hashem will make his face shine in the world to come, and about this time the verse states, ‘And the successful ones will shine like the sky above, those who caused others merits will be like eternal stars, and those who loved Him will be like the sun rising in full strength’. Some people will shine like the sky, some like stars, and some like the sun. Even those who will shine like the sun will shine with various degrees of light, just as the sun is not as strong when it rises as it is a few hours later, and those who love Hashem will shine like the sun at noon. At that time it will be completely evident who is righteous and who is wicked, and even among the righteous the differences will be pronounced, as our Sages taught that there will be a tremendous difference between someone who repeated what he learned one hundred times, to the one who repeated it even one time more. The difference between one who learned a whole subject of Torah that the other did not learn at all will be pronounced sevenfold, and this will cause tremendous anguish to the one who failed to learn it, but it will be too late.
כ״ז באלול ה׳תשפ״ב
"והאמת בלתי שום ספק כלל, שאם היה העולם כולו מקצה עד קצהו פנוי חס ושלום אף רגע אחד ממש מהעסק והתבוננות שלנו בתורה, כרגע היו נחרבים כל העולמות, עליונים ותחתונים, והיו לאפס ותוהו חס ושלום". (נפש החיים) 1