The Torah reading of Parah (Numbers 19) details the laws of the “Red Heifer” and the process by which a person rendered ritually impure by contact with a dead body was purified.
We fulfill the Temple-related rituals by studying their laws in the Torah. When the Holy Temple stood in Jerusalem, every Jew had to be in a state of ritual purity in time for the bringing of the Passover offering in the Temple. Today, though we’re unable to fulfill the Temple-related rituals in practice, we fulfill them spiritually by studying their laws in the Torah. Thus, we study and read the section of Parah in preparation for the upcoming festival of Passover.
According to some Halachic authorities, there is a Biblical requirement for all men to hear the special Parah reading.
The special Parah haftarah (Ezekiel 36:16-36) discusses Gd’s promise to “purify” and cleanse the Jews when He re-gathers them and returns them all to the Land of Israel during the Messianic Era.
The Hachodesh reading (Exodus 12:1-20) recounts Gd’s historic communication to Moses in Egypt on the first of Nissan, two weeks before the Exodus, regarding the establishment of a Jewish (lunar) calendar, the Paschal Offering, matzah, bitter herbs, and the seder.
The special Hachodesh haftorah (Ezekiel 45:18-46:15) is a prophecy regarding the Paschal Offering that will be brought in the Third Holy Temple.
Article courtesy of Chabad.org