What do we learn from "ha'Sa'if Einecha Bo v'Einenu"?
Malbim citing Sotah 35a: This refers to Divrei Torah. Wink your eye (for one moment, neglect) them, and they are gone 1 . Rashi - [if you try to learn bundles and bundles of teachings,] in the moment to blink an eye, you lose [forget] it. The Targum of "v'Chafalta" (Shemos 26:9, you will fold) is v'Sei'uf.
R. Yonah: Even if you will attain wealth, perhaps you will not keep it. It can be lost in the time of an eye's blink. The prefix Hei in ha'Sa'if is to verify the matter, like "ha'Niglah Nigleisi" (Shmuel I, 2:27). These two verses are next to what came above, that one should not strive to follow the king in order to become rich.
Malbim: You must not hide your eye from your Binah, even for a moment. It is like a flying bird in man's hand. In a moment it turns from him to fly above. So man's intellect and Tevunah, if he ignores them for a moment, they fly from him. If you will cover your eye with your eyelid, your Binah will depart. It will get wings to fly from you.
Ma'alos ha'Torah (DH Davar Acher): If one forgets the first matters that he learns, also what he learns later will not endure - "v'Hayah Im Shacho'ach Tishkach" (Devarim 8:14). It is written in Megilas Chasidim - if you abandon Me one day, I will abandon you two days.
