A year after the Exodus from Egypt, God instructed the Jewish people to bring the Passover offering on the night of the 14th of Nisan and eat it that night roasted over a fire, along with matzah and bitter herbs. "However, there were some people ritually unclean because of contact with a dead body, and they could not prepare the Passover offering that day. They approached Moses and Aaron and said, '...why should we be left out and not be able to bring the offering to God at the appointed time, along with the rest of the Jewish people?'" (Deuteronomy 9).
In response to their request, God established the 14th of Iyar (one month after Passover) as the "Second Passover" for all those people who were unable to bring the offering on Passover.
That day represents the "second chance", teaching us that all is never lost.