Commentary for Numbers 23:12

הלא את אשר ישים ה' בפי, you already know that He is the G’d of Israel, and that therefore He will only speak well of the Israelites.

הלא את אשר ישים ה׳ בפי, "Did I not tell you that whatever G'd will put into my mouth, etc." Bileam explained that Balak had erred when he thought that Bileam would not be obligated to utter blessings if G'd put these into his mouth. He was not free to shut his mouth and refuse to speak. This is why he added the word אשמר. We have learned in Shevuot 36 that the words ,השמר פן and אל are formulations preceding a negative commandment, and that if one ignores a commandment preceded by these words (by remaining silent) one may become liable to the death penalty. We have not heard previously that Bileam was under such a restriction. Our sages in Tanchuma 12 explain that Bileam said to G'd he would rather die than to be guilty of cursing the Israelites when he realised that G'd watched every move he made. This was the meaning of "may my soul die, etc." However, he acted under duress having become only G'd's mouthpiece.

We may also understand Bileam's reply in terms of the Yalkut we quoted earlier that G'd put a bar in Bileam's mouth. When he wanted to curse G'd would twist the bar to make this impossible. He could only feel comfortable physically by complying with G'd's instructions. Otherwise he would become mute.

It is also possible that he told Balak that he was hoping G'd would put His words in his mouth, and this was why he spoke about אשר ישים ה׳ בפי, "what G'd is going to put into my mouth I will guard carefully." This is the reason he did not say: "what G'd has put in my mouth." He told Balak that although G'd had put restrictions on what he could say, he looked forward to uttering G'd's holy words even under the forced conditions. He considered it a privilege to become G'd's mouthpiece.