Rabbi Gedalia Kauffman
The Zohar teaches that the pious people of the earlier generations would stay awake all night [on Shavuot] learning Torah.
(Magen Avraham, 494:1)
איתא בזוהר שחסידים הראשונים היו נעורים כל הלילה ועוסקים בתורה.
(מגן אברהם, תצד:א)
There is a widespread custom on Shavuos to remain awake the entire night learning Torah. The origin of this custom is ancient. The Zohar1 tells us it was already in practice amongst the very righteous two thousand years ago. The great kabbalist, the Ari, says that anyone who follows this custom, learns with seriousness and does not sleep at all is assured that he will live out the rest of the year without any harm befalling him.2
But this custom seems puzzling. To anyone who has stayed up on Shavuos night, it is apparent that as the night goes on the quality of the learning declines. Fatigue sets in and it becomes difficult to focus, especially on complex Torah topics. To make matters worse, after an exceedingly long night everyone sleeps away the entire morning and wakes up feeling exhausted in the afternoon. As a result, little Torah learning takes place on Shavuos day. Surely there is a better way. If we were to get a good night’s sleep and wake up early would it not improve both the quality and the quantity of our learning?
Someone who needs to catch an early morning flight may find himself waking up with a start multiple times during the night to check the time. If something is important to you then you make very certain NOT to be late. Yet, the Midrash3 tells us that on the morning of the Revelation at Sinai the Jewish people overslept. To be late for a meeting with G-d to receive His Torah reflects a serious lack of appreciation for the incredible gift of Torah.
If the goal is to learn as much Torah as possible then staying up all night makes little sense. But the true purpose of staying up is to show our anticipation and enthusiasm for the receiving of the Torah. On Shavuos, Hashem is offering us the Torah once again. Regardless of whether we manage to learn the entire night, He wants to see our anticipation and excitement. He wants to know that we appreciate the beauty and the power of the Torah that He is offering us. With that energy and enthusiasm, we can re-commit ourselves to Torah learning and merit to once again receive our portion in Torah for the coming year.
Zohar, Vol. I 8a, Vol. III 97b-98a; brought by Magen Avraham 494:1; Mishnah Berurah 494:1
See Mishnah Berurah 494:1
Midrash, Pirkei DeRabbi Eliezer 41:7; Midrash, Shir HaShirim Rabbah 1:12