The passuk states: Hashem says to Moshe ועתה הניחה לי… ואכלם and now “leave” Me… and I will destroy them. Similarly in Parshas Eikev it states הרף ממני ואשמידם “loosen up from Me” and I will destroy them. Onkelos translates both הניחה and הרף as “leave, put down your davening” which seems to say that Moshe was davening to Hashem to forgive Yisrael. This is as the Gemara brings, Rebi Avahu said: since the passuk states הניחה לי, this reflects that Moshe took hold of Hashem as a person who grabs his friend’s garment. Moshe said, “I will not leave You until You forgive them.” Moshe started to daven to Hashem on behalf of the Bnei Yisrael to stop the decree of destroying all of Yisrael, and succeeded; Hashem accepted his davening. The Nefesh HaGer explains that in Sefer Devarim, where Moshe repeated the Torah, Moshe did not say the lashon הניחה because he did not want to state about himself that he took hold of Hashem.
Rashi explains that Moshe did not start davening on behalf of Yisrael. Hashem said ועתה הניחה לי “and now leave Me” to reflect that Hashem showed Moshe an opening, and let him know that it is dependent on him, that if he will daven on behalf of Yisrael, He won’t destroy them. This is as the Gemara brings Rebi Eliezer said: Hashem said to Moshe, “לך רד go down from your greatness. I only gave you greatness because of Yisrael, now that they sinned what greatness do you need?” Immediately Moshe’s strength weakened and he did not have energy to speak. Once Hashem said הרף ממני ואשמידם “loosen up from Me and I will destroy them” Moshe said, “it is dependent upon me.” Immediately he stood up and strengthened himself with davening and asked for Hashem’s mercy. This is similar to a king who got angry at his son and hit him hard. The king’s good friend was sitting there and was afraid to say anything. The king said, “if not for my good friend sitting here I would kill him.” Once the friend recognized that it was dependent on him, he immediately stood up and saved the king’s son. So too with Moshe, once he realized it was dependent on him, he davened for Yisrael and saved them.
The Maharsha explains that it seems from these two Gemaros that there are two opinions whether Moshe started to daven on his own or only started to daven after Hashem showed him that it was dependent on him. However, since the Gemara does not mention that they argue, it seems that all the opinions coincide. The Maharsha explains that originally Moshe did not think to daven to Hashem assuming there was no hope. Hashem said הרף ממני showing Moshe that there was place to daven and it indeed depended on him. Moshe then immediately starting to daven to Hashem. Afterwards Hashem said, “הניחה לי leave Me, stop so I can destroy Yisrael,” however Moshe continued even so, until Hashem accepted his davening, and forgave them.
We see that although Hashem decreed to destroy Yisrael, Moshe’s davening helped cause Hashem to forgive them. Moshe did not let go, and was able to change Hashem’s decision to destroy Yisrael. This teaches the tremendous power of davening no matter what. One should never give up hope and daven to Hashem for His salvation!