Rosh Chodesh Nissan is one of the most significant days in all of history. On that day, G-d gave us the first mitzvah, the mitzvah of declaring and sanctifying the new month. For 2,448 years, G-d did so Himself, but on that day He entrusted this honor and responsibility to the Jewish people.

Why is this mitzvah so significant? Because it shows that we have the ability — and responsibility — to sanctify our lives and the passage of time. By giving us the power to change and determine physical reality, He made us His partners in the ongoing process of creation.

In order to commemorate this new period in history, Nissan is counted as the first month on the Jewish calendar.