The significance of Rosh Chodesh…as found on OU website.
(Material below is adapted from Mesorah Publications’ Stone Edition of the Chumash)
“This is the very first commandment given to the nation as a whole, an indication that the concept of Rosh Chadesh, or New Moon, is very meaningful. Moreover, a thousand years later in Eretz Yisrael, during the period of Syrian-Greek persecution that culminated in the miracle of Chanukah, Rosh Chodesh was one of only three commandments whose observance the oppressors prohibitied. The other two forbidden commandments were the Sabbath and circumcision; that Rosh Chodesh was on a plane with these central observances is sufficient indication of its great significance.”
“This can be understood on two levels, As will be noted below, only the court can proclaim Rosh Chodesh based on the testimony of witnesses who observed the re-appearance of the moon, and upon this proclamation, the Jewish calendar is based. Unless the new months can be claimed there is no calendar, and without a calendar, there can be no festivals. Thus, if the Syrian-Greeks had succeeded in eradication the observance of Rosh Chodesh, they would have succeeded in in eliminating large numbers of other mitzot, as well.”
“On a deeper level, Rosh Chodesh symbolises renewal, the ability of the Jewish People to rise up from oblivion and restore itself to its past greatness. Just as the moon disappears at the end of each month, but returns and grows to fullness. so Israel may suffer exile and decline, but it always renews itself. – until the coming of the Messiah, when the promise of the Exodus and the revelation at Sinai will be fulfilled, never to be dimmed again.”
“This essential characteristic of Jewish history was first exhibited in Egypt, when, in the simile of the Sages, the nation had fallen to the forty-ninth level of impurity – one level above spiritual extermination – only to renew itself so breathtakingly that after seven weeks it was able to stand at Mount Sinai and experience prophecy.”
“This concept of Jewish renewal was what the Syrian-Greeks attempted to eradicate by ending the observance of Rosh Chodesh. Instead, the Jewish People rose up in defence of the Torah and the Temple, and their triumph is commemmorated through Chanuka, the festival of renewal.”