The awareness that God extends His providence to the actions of human beings makes those who are devoted to Him rejoice in their good deeds, and likewise, it makes them ashamed of their evil deeds. In contrast to the handiwork of a human being, which exists even when it is separated from the one who produced it, creation is perpetually connected to God; this is divine providence. If God withdrew His providence from creation, the entire world would be destroyed.

An eye that sees:

A pious person does not perform one act, think one thought, or speak one word, without [considering] his belief that there is an eye that sees him, repays him for the good and for the bad, and calls him to account for anything objectionable in his speech or actions. Therefore, he walks and sits as one in awe. He trembles and is at times ashamed of his actions, just as he rejoices and delights, and his spirit is elevated, when he does good…. As a result of his faith, a pious person fulfills the saying of the Sages, “Keep your eye on three things, and you will not come to sin: Know what is above you: An eye that sees, and an ear that hears, and that all your deeds are recorded in a book” (Mishna Avot 2:1).

The difference between the handiwork of humans and the creations of God:

No part of creation is like the product of human labor. A person labors, for example, to build a mill. Even when he leaves it, the mill will continue to do the work it was designed for. The Creator, on the other hand, creates every organ and designates abilities to each one, and He also controls these abilities at every instant. Imagine Him removing His providence from them for one moment: The entire world would be lost. (Rav Yehuda HaLevi, Kuzari 3:11)

Further reading: For more on the importance of reflecting on the fact that God is watching over us and sees all of our actions, see p. 192; A Concise Guide to the Sages, p. 367.