When the Jewish people came out of Mitzrayim many of them still had a pagen mindset. This mindset comforted them in worshipping death, and a life in the world to come, over truly living in the world which they physically walked.
Many pagan religions, and even some religions today, worship the comfort of death and a life in a world to come over the hear and now.
The worship of the golden calf, that the Jewish people made and worshiped as a replacement for their leader Moshe, and as a symbolic connector to G-d, symbolizes death. With the act of building and worshiping the golden calf, the calf itself becomes a representation for disconnection and separation from the physical world in which they live and the laws an statutes which they pledged to follow.
Hashem, through his wisdom, transformed the cow from a symbol of death into the life affirming symbol. Through the ritual of the sprinkling of the ashes of the red heifer (known as the parah adumah), in order to cleanse oneself after coming in contact with death, an animal once used in separation and disconnection to the world around becomes important in daily life, as a representation and reminder of the importance of living.
Hashem, through the Torah, stresses for us the importance of living a G-dly existence here on earth. The main purpose of our existence is not to reach a world to come, but to do G-d’s will here on earth and live a life worthy of Hashem’s praises. Chassidus and kabbalah teaches us that our existence here on earth is of the utmost important, and when we live a life centred on Torah and mitzvoth, and thorough the act of elevating the mundane to the status of holy, we can create a world of holiness. This holiness allows for Hashem to come a dwell amongst us, and how much more life affirming can we get than this?
But if the above mentioned life affirming examples are not enough, the Torah not only symbolically stress the importance of life, it explicitly show us the transcending importance of life over death through the principle of Pikuach Nefesh – saving a life (Vayikra 19:16, parshat Kedoshim “Neither shall you stand by the blood of your neighbor”). This principal takes precedence over almost every other Torah commandment and reaffirms the importance of living over dying.
So, even though the worship of the golden calf was a symbol for death, through the commandment of the parah adumah the cow is turned into a symbol of the reaffirmed importance of life. Gut Shabbos.