“Who may ascend the mountain of G-d, and who may stand in His holy place. He who has clean hands and a pure heart, who has not sworn in vain by My soul and has not sworn deceitfully.”1
To swear falsely is one of the many transgressions Torah forbids; why would the particular virtue of avoiding false oaths qualify as sufficient merit to ascend the mountain of G-d?
The Talmud2 says that before a child leaves the womb to enter the world, an oath is administered to him: “Be a righteous person and not a wicked one.” The “oath” is also explained in terms of a delegation of power to the soul so that it be able to fulfill its destiny in life on earth.3
This Psalm is referring to this prenatal oath. One who honors this significant oath, i.e. one who fulfills the oath he took as an unborn child and strives to develop into a righteous person over the course of his life, did not take the oath deceitfully and is thus qualified to be among those who merit to “ascend the mountain of G-d.”
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This Psalm is recited on Rosh Hashanah and Yom Kippur after the the evening Amidah, is a vessel through which one elicits material success for the entire year. Thus, it should be said with proper thought and intention.4