The Chafetz Chaim raised his holy finger upward and explained: “Up there, He sees very well... It is a clear teaching in Pirkei Avos (2:1), “Know what is above you—an eye that sees! For the whole earth is filled with His glory (Yeshayah 6:3), and there is no place empty of Him.”
Woe unto us from the Day of Judgment, woe unto us from the Day of Rebuke!
In the manner of this story we may understand the simple meaning of the pasuk (Tehillim 33:13), From Heaven Hashem gazes; He sees all the children of man. For this is the foundation and root of the faith of holy Yisrael: nothing is hidden from Hashem, and the Borei Yisbarach, rewards those who keep His commandments and punishes those who transgress them.
This pasuk should be repeated constantly: From Heaven Hashem gazes; He sees all the children of man! One must fix this in his heart—that even if he acts in secret, in darkness, Hashem sees him. As it says (Yirmiyahu 23:24), אִם יִסָּתֵר אִישׁ בַּמִּסְתָּרִים וַאֲנִי ‘ הֲלוֹא אֶת הַשָּׁמַיִם וְאֶת הָאָרֶץ אֲנִילֹא אֶרְאֶנּוּ נְאֻם ה מָלֵא נְאֻם ה› Can a man hide in hidden places and I will not see him—says Hashem? Look, I fill the heavens and the earth—says Hashem.
Through this one merits the acquisition of true yiras Shamayim.