In a previous Dvar Torah, I expressed my opinion that the single most important halacha within the ten chapters and sixty-nine halachot of Maimonides' Laws of Repentance is what he writes in chapter 3, halacha 4:

Throughout the entire year, a person must look at himself as being equally balanced between merit and sin, and the entire world as being equally balanced between merit and sin. If he performs one sin, he tips his balance and that of the entire world to the side of guilt and brings destruction upon himself; if he performs one mitzva, he tips his balance and that of the entire world to the side of merit and brings deliverance and salvation to himself and to others, as the verse says: "A righteous man is the foundation of the world," [Proverbs 10:25] that is, he who acted righteously, tipped the balance of the entire world to merit and saved it.
Rebbe Levi Yitzḥak of Berdichev (1740 - 1809) connects this halacha to the Mishnaic statement:
Everyone is obligated to say "for my sake was the world created." (We may note that the version of Tanna d'Bei Eliyahu [a midrash attributed to the prophet Elijah and quoted a number of times in the Talmud] is "every Israelite is obligated to say 'for my sake was the world created'.")
Thus writes Rebbe Levi Yitzḥak:
The main factor which brings one to fear of Heaven is the constant awareness that the entire world depends upon his actions, as our Sages stated "Everyone is obligated to say 'for my sake was the world created'." and one must always see himself as being equally balanced between merit and sin … if he adds a single merit, he has tipped the balance of the entire world to merit. Thus, when one reflects on the fact that the entire world depends upon his deeds, and was created for him, he will bitterly regret his sins and he will be enthusiastic about God's mitzvot and His Torah, in order to bring abundance to all the worlds, all the angels and all the souls of the lower world.
At first glance, the Mishna's statement can be seen as an expression of arrogance, hubris and pretension; however, our Sages intended that the Israelite make this statement as acceptance of responsibility. In commenting on Maimonides' words, Rabbi Adin Even-Yisrael (Steinsaltz) writes that the intention is that the individual see himself as bearing the full responsibility (for the entire world). Indeed, one who truly sees himself as responsible for the entire world will take great care in his behavior, increasing the mitzvot he performs and minimizing his sins, in order to tip the balance for his own benefit and the benefit of the world.
The kabbalist Rabbi Menaḥem Recanati (1250 – 1310) adds two words to the Mishna's statement:

Every Israelite is obligated to say to himself "for my sake was the world created." [commentary on Genesis 17:1]
Were a person to make the statement to another, it would indeed be most arrogant; but in saying it to oneself, the intent is recognition of one's responsibility for the entire world. (David Magence)

Shabbat Shalom and G’mar Chatima Tova!
The Va’ad