That is that He commanded us to swear by His name when it is necessary to ratify something or to deny it. For there is aggrandizement, glory and exhalation through this. And that is His, may He be blessed, saying, "and by His name shall you swear" (Deuteronomy 10:20). And in the explanation, they said, "The Torah said, 'Swear,' and the Torah said, 'Do not swear' - meaning to say, just like it prohibits an oath for which there is no need, and it is a negative commandment; so too is there a commandment [to make] an oath when it is needed, and it is a positive commandment. And as a result, it is not permitted to swear by any of all the creatures, such as the angels or the stars, except by way of nullifying what is attached. This is like one who swears by the sun, but he means to say, the Master of the sun. And in this way, our nation swears by the name of our teacher, Moshe - how glorious is his name - as if the one swearing was swearing by the Master or by the One who sent him.

Whoever recites a blessing for which he is not obligated is considered as if he took God's name in vain. He is considered as one who took a false oath, and it is forbidden to answer Amen after his blessing.

THOU SHALT NOT TAKE THE NAME OF THE LORD THY GOD IN VAIN.

... Now when a person mentions God’s name he is saying, as God is True so is what I will say true. Thus if he does not keep his word, he is, as it were, denying God. It is still the custom in Egypt for one to incur the death penalty if he swears by the head of the king and does not keep his word. The culprit is not spared even if he gives his ransom in gold because he publicly insulted the king. If this is the case with regard to a king of flesh and blood, how many thousands of times more does one have to be careful that one’s mouth does not cause his tongue to stumble and bring his flesh into guilt by mentioning God’s name in vain.

The sum of the matter is that with the exception of honoring one’s parents, we do not find the reward for observing a commandment clearly spelled out in any of the Ten Statements. We similarly do not find the punishment for violating a commandment spelled out except for idolatry and taking God’s name in vain. Many think that a person who takes the name of the Lord in vain does not commit a great sin. I will show that in reality it is more severe than any of the other prohibitions which follow. For a murderer cannot commit murder, nor an adulterer adultery, both of which are major sins, whenever they want to because they are afraid of being caught. However, the person who is the habit of swearing falsely will daily utter innumerable vows. Such a person is so accustomed to committing this sin that he is not even aware that he is taking an oath. Should someone chide him and say to him, “Why are you swearing?” he responds by swearing that he did not swear, because he is so habituated to swearing. For he prefaces anything he says by saying, “I swear.” They think that this is an elegant way to speak. If Israel was guilty only of this sin it would be cause enough to prolong the exile and add blows to our blows.