On the 14th of Nisan, 2449 – two weeks after the inauguration of the Tabernacle – G‑d commanded the Jewish people to observe the holiday of Passover. (Since G‑d had previously told the Jews that they would not be required to observe the festivals until entering the Land of Israel, this exceptional case necessitated an explicit command.) However, some of the people were ritually defiled and therefore unable to participate in the festival. They complained about being left out, and in response, G‑d informed the people that whoever was unable to perform the Passover rituals on the date of the holiday should perform them a month later, on the 14th of Iyar.
It’s Never Too Late
בַּחֹדֶשׁ הַשֵּׁנִי בְּאַרְבָּעָה עָשָׂר יוֹם . . . יַעֲשׂוּ אֹתוֹ וגו'ּ: (במדבר ט:יא)
[G‑d told Moses,] “[If someone was unable to offer up the Passover sacrifice on the 14th day of Nisan,] he must offer it up in the afternoon of the 14th day of [Iyar,] the second month.” Numbers 9:11

The lesson of the second Passover is that it is never too late to set things right. Even if one is spiritually sullied or has wandered far from the realm of holiness, G‑d still gives him a fresh opportunity to rewrite the past and to right all wrongs.1