Why does the Torah juxtapose "Shiv'as Yamim" to "Tishmor"?
Chagigah, 18a: To teach us that Chol ha'Mo'ed is included in the Isur Melachah on Yom-Tov. 1
See Torah Temimah, note 97
Why is Nisan called "Chodesh ha'Aviv"?
Rashi #1: Nisan is the month when the grain ripens on its stalks ('be'Ivehah'. 1
Rashi #2: It means father (Av), since it is the father of the months, in that it is the month whien the fruits first ripen.
Torah Temimah (in Devarim 16:1, citing the Sifri): Hashem deliberately took us out of Egypt in the month of spring, the ideal month to travel, since it is neither too hot nor too cold. 4 Refer to 13:4:1:1*.
What are the implications of "be'Mo'ed Chodesh ha'Aviv"?
Mechilta: It implies that Pesach fall in the spring. Consequently, in order to ensure that it does, it is sometimes necessary to declare a leap-year.
What are the connotations of "ve'Lo Yera'u Panai Reikam"?
Oznayim la'Torah: It is to commemprate Yetzi'as Mitzrayim, where Hashem told Yisrael "Lo Seilchu Reikam"
Chagigah, 7a: Specifically Olos
What are the implications of "Reikam"?
Yerushalmi Pe'ah, 1:5: It implies that the Olas Re'iyah has no minimum Shi'ur and is Kasher irrespective of how little it costs.