The LORD said to Moses and Aaron in the land of Egypt, “This month shall be for you the beginning of months. It shall be the first month of the year for you.” (Exodus 12:1-2)
On the Jewish calendar Nisan is the first month of the liturgical calendar and the seventh month of the civil calendar. Rabbi Joshua teaches that all three patriarchs were born and died in the month of Nisan and that the world was created on Nisan 1. 
This is also, of course, the month in which we celebrate Passover and the death and resurrection of our Master. The Talmud teaches: “In Nisan the bondage of our ancestors ceased in Egypt; and in Nisan they will be redeemed in time to come.” 
Originally, because this month takes place in the spring in Israel and the northern hemisphere, it was called Aviv which means spring. However, after the Babylonian captivity it is henceforth referred to as Nisan.  The word Nisan itself is also connected to spring-like imagery. Some rabbis have connected it to the word nitzan, which refers to a shoot of new plant life that breaks through the ground.  Indeed, Nisan is a month of new life breaking through both physically and spiritually.
Rosh Chodesh is a time of renewal. Just as the moon is made new again so there is a spiritual power present at that time for us to begin again and transform our lives. But Rosh Chodesh Nisan is even more special:
The cycle of months begins with Rosh Chodesh Nissan. Every Rosh Chodesh contains the power of renewal, as manifest in the renewal of the moon. Rosh Chodesh Nissan, the crown of all Roshei Chadashim, contains an extra-special power of renewal. This is manifest in the renewal of the entire natural world at this time. Refreshed by the rains of winter, the plants and animals all begin a new cycle of growth. 
In Nisan we begin to see new life all around us and this represents the potential for change that exists around us. The sages also speak of Nisan as a time of song:
Rabbi Eleazar and Rabbi Simeon said: When do the rams mount the sheep? At the time when they [the ears of corn] shout for joy and sing. [Psalm 65:14]. When do the ears of corn burst into song? In Nisan. (b.Rosh HaShanah 8a)
All around us nature is singing. From the song of the birds returning from their migration, the ripples of a brook that is thawing out, to crickets and frogs breaking the silence of the night with their sounds. For us, too, it is a time of singing, which is culminated in the songs of the Haggadah and the Hallel.
Rabbi Nosson Slifkin said that the quintessential creature that represents spring is the gazelle: 
The voice of my beloved! Behold, he comes, leaping over the mountains, bounding over the hills. My beloved is like a gazelle or a young stag. Behold, there he stands behind our wall, gazing through the windows, looking through the lattice. (Song of Songs 2:8-9)
The swiftness with which the gazelle moves mirrors the swiftness of the newness of life as it burst forth in the spring. The sages even say, “Run like a gazelle to do the will of your father in heaven” (m.Avot 5:24). Hence, Nisan carries with it a speed of renewal unlike any other time of the year.
Rosh Chodesh Nisan and the entire month represents an enormous potential for spiritual transformation and joy. Although every day represents a new beginning and a chance to start fresh, these thirty days of Nisan bring with them the power of transformation that is unparalleled throughout the rest of the year. After all, it was in the month of Nisan that our Master rose from the dead and extended to Israel and the world the gift of eternal life. As we begin cleaning and preparing for Passover, may Nisan be a month of spiritual growth and renewal for all of us like never before. May we run to do the will of our Father in heaven while our mouth is filled with songs of joy!
- b.Rosh HaShanah 10b-11a.
- Ibid., 11a.
- Exodus 13:4, 23:15; Nehemiah 2:1; Esther 3:7.
- Rabbi Nosson Slifkin, Seasons of Life: The Reflection of the Jewish Year in the Natural World (Southfield, MI: Targum Press, 1998), 85.
- Ibid., 81.
- This is the Hebrew word tzvi, which is sometimes translated as “antelope.”