The Midrash (Shemos 15:2) states: Malachim ask Hakadosh Baruch Hu, "Ribono Shel Olam, when will You make yom tov...?" Hakadosh Baruch Hu replies, "Me and you will agree to whatever the Jewish nation decides..." Hakadosh Baruch Hu says to Bnei Yisrael, "In the past, it was in My hands... From now on it is in your hands. When you say yes, it is yes. When you say no, it is no. החודש לכם הזה, the new month is up to you. And even if you want to have a leap year, I accede to your judgment...’”
The Chidushei HaRim zt’l taught this Midrash and expressed, “Everything was given over to us! Everything is in our hands! If a person knows this and discovers who he is and what is his potential, he won’t waste a moment.”
לכם הזה החודש teaches us a fundamental concept. Hashem gave over rosh chodesh, leap years, and ultimately everything into our hands. Hashem and the malachim take counsel from and hearken to the decisions of Klal Yisrael. This tells us that the Jewish nation is also empowered with the power of tefillah. This is implied in the words of the Midrash, "When you say yes, it is yes. When you say no, it is no." The Jewish nation was given immense power and influence.
