Halakha Imamat 19:12: Mishneh Torah, Foundations, Sefer HaChinukh & Mishneh Torah, Negative Mitzvot

Whosoever willfully, without duress, will transgress one of the commandments of the Torah, because he despises it and does so spitefully, behold, he is blaspheming the Name. Therefore, it is said of false swearing: "Thou hast hereby defiled the name of thy God; I am the Lord" (Lev. 19. 12). And if he commits the offense in the presence of ten Israelites, he is guilty of public blasphemy. Conversely, if one abstains from sin, or fulfills a commandment without ulterior motive, not because of terror or fear, nor in pursuit of honor, but merely for the sake of the Creator, blessed is He! Even as Joseph the Pious did resist the temptation of his master's wife, behold, he doth sanctify the Name of God.

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.

(We are charged) not to blaspheme, as it is said, “Thou shalt not revile God” (Ex. 22:27); and in regard to the penalty, it is said, “And he that blasphemeth the name of the Lord shall surely be put to death” (Lev. 24:16). The general principle is that wherever the Scripture prescribes the penalty of excision or a judicial sentence of capital punishment, the offence is the violation of a prohibition. The only exceptions are Circumcision and the Passover, which are affirmative precepts, while their neglect involves the penalty of excision.