The big things of this mitzva include the process of Kiddush HaChodesh in the time of Sanhedrin (past and future). The details of eye-witness testimony to the first visibility of the lunar crescent. Traveling to Jerusalem to testify even on Friday night. The significance of the sanctification of the first day of the month to the sanctity - and very existence - of the Chagim and Yamim Nora'im. The fact that Kiddush HaChodesh was a major target of the Greek persecution of the pre-Chanuka era. The big things. Sanhedrin. Beit HaMikdash. Korbanot.
But there are little things too. And these can be and should be very special to each of us. Do you know today's Hebrew (Jewish) date? Do you mark your family members' birthdays on the Jewish calendar (in addition or not to the secular date)? And here's another "little" thing for those of us living in Israel - How do you date your checks? We can look at it like this: What G-d was saying to the Jewish People while we were still in Egypt was that as a nation - His nation - we will have a distinct calendar. We will remain cognizant of the world around us and their way of reckoning time, but the Jewish Calendar is a Divine gift from G-d to us. It is so much ours, that if and when we make a mistake in declaring the "wrong" day as Rosh Chodesh, G-d (so to speak) throws His calendar out and takes our flawed one instead. That's a big thought again, but let's refocus on the little things. Does it not behoove us to know the Jewish Calendar well, because G-d gave it to us.
Our very first mitzva as a new People. Does it not behoove us to celebrate our birthdays in the Jewish Calendar that we got from the One who also gave us Life? And what a special idea to fulfill a little of HaChodesh HaZeh Lachem every time we sign a check. How about it?