בַּחֹדֶשׁ הַזֶּה. שִׁבְעַת יָמִים, תֹּאכַל מַצֹּת
and this may be taken as a hint, as follows. It talks about seven days, which are the seven days of the week. The first day of this week, a week of eating Matzot, may start on seven possible dates: הא"ה, הב"ה, הג"ה, הד"ה, הה"ה, הו"ה, הז"ה of Nissan. And "Chag HaPesach" is the seventh day of this week:וּבַיּוֹם, הַשְּׁבִיעִי, חַג, לַיהוָה
So the dates of Pesach are Nissan 17 through Nissan 23. This is different from what it says in P and D, who want the Chag to fall on the full moon, Nissan 15, as we all know. However, the Torah Kedumah denies the relevance of the Moon, the Sun, and the stars. This year, Pesach would, according to the above, fall on Nissan 22, after a week of eating Matzot starting on Nissan 16.In my understanding, Chag Shavuot, HaKatzir, would be seven weeks after Pesach, whereas Chag HaAsif, Sukkot, is parallel to the above.
The Halacha regarding the date of Pesach, is according to P (and D). This was a victory for the Yetzer HaRa, which is one of the causes of the long exile. Only in the scientific age, no one seriously believes anymore in the forces of the Moon, that once had a feverish following. Therefore, the dispute has, at long last, become a moot point, and there is now no reason to change the Halacha on this issue.
