Halakhah su Salmi 31:19

And from this root itself is the matter of a false oath (shevuah), meaning to say when he swears to fulfill something and does not fulfill it. [This] is called an oath of speech, about which another separate commandment comes in the Order of Kedoshim Tehiyu, as it is stated (Leviticus 19:12), "And you shall not swear falsely by My name." As one who swears by the great name [of God] to say something was and [yet] he knows that there is falsehood in his mouth, behold, he is acting lightly with the awe of God; as if to say in his heart that He is not true - 'let his lips be silent.' And so the one who swears to do something and afterwards does not do it is, behold, also among the rebels against light, the deniers of truth. As the understanding of "swore," is, according to my opinion, that he concludes in his heart and says with his mouth to fulfill that thing that he swore about and that he will never change it, [just] as God, may He be blessed, exists and does not change forever and ever. And that is [why] the expression, sworn nishbaa always comes in the passive; meaning to say that he is acted upon by his words to make it exist, [just] like he said about His existence, blessed be He.