[Rav Wolbe would say that the Ramban at the end of Parsha Bo (Shemos 13, 16) lays down some of the most basic ideas regarding Judaism and that everyone should know this Ramban by heart!]
"Now I will tell you a rule that will explain the reason behind many mitzvos: From the onset of idol worship in the days of Enosh, people's beliefs became confused. There were those who denied the Creator and claimed that the world always existed. And there were those who denied His knowledge of what occurs on earth; they said, 'How can G-d know - Does the One Above has knowledge?' (Tehillim 73, 11). Additionally, there were those who agreed that Hashem knows about the earthly occurrences but they thought that He does not involve Himself in the running of the world. 'They considered men similar to fish' (Chabakuk 1, 14) - Hashem does not watch over them and there is no punishment or reward for their actions. They claimed, 'Hashem has abandoned the land' (Yechezkel 8, 12).
"Hence, when Hashem shows interest in a nation or an individual and performs wonders whereby He changes the course of nature, it becomes clear to one and all the fallacy of the above claims. An awesome miracle proves that there is a G-d Who creates the world, Who knows, is involved and is Omnipotent. And when a prophet predicts a miracle, there is an additional advantage: the truth of prophecy becomes apparent, that Hashem speaks to man and reveals His secrets to His servants, the prophets. This lends credence to the entire Torah (since believing that the Torah came from Heaven is dependent upon believing that Hashem speaks to man).
"Therefore, with regard to the miracles (i.e. the plagues) the Torah writes, 'So that you should know that I am Hashem in the midst of the land' (Shemos 8, 18) - to prove that Hashem is involved and has not disengaged from the world, letting it run its own course. It is likewise written, 'So that you should know that the land belongs to Hashem' (ibid. 9, 29) - verifying that Hashem is their Creator and He created them from nothing. Additionally, the Torah writes, 'So that you know that there is no one like Me in the entire land' (ibid. 9, 14) - to assert His Omnipotence - He rules over everything and there is no one who can inhibit His ability to do as He pleases. [Hashem brought about all the plagues] because the Egyptians denied or were uncertain about these truths. It follows that great miracles and wonders are true witnesses verifying belief in the Creator and the entire Torah.
"However, since Hashem will not perform a miracle in every generation for every wicked person or non-believer, He commanded us to make constant reminders to help us remember the events that we witnessed. And we are to relay this message to our children and they to their children until the end of days. The great importance of this idea is apparent, for one who eats chametz on Pesach or disregards the commandment of the korban Pesach, is punished with kares. Also, He required that we write all the wonders that we witnessed upon our arms and between our eyes (tefillin) and upon our doorposts (mezuzah). And we are to verbally remember it twice daily - in the morning and evening - as our Sages said, "Emes V'yatziv is a Torah commandment, for the pasuk says, 'You shall remember Yetzias Mitzrayim all the days of your life.'" Likewise, He commanded us to build a sukkah each year and to perform numerous mitzvos "zecher l'yitziyas Mitzrayim."
"The purpose of all these mitzvos is to bear witness in every generation to the miracles, lest they be forgotten, so that non-believers will not have the ability to open their mouths in denial. He who buys a mezuzah for few coins, affixes it to his doorpost and contemplates the reason behind it, has already acknowledged that the world was [a] new [creation] and that the Creator knows what is occurring and is involved in every aspect. He has also acknowledged that there is prophecy and manifested his belief in the entire Torah. Moreover, he has acknowledged Hashem's kindness toward those who perform His will - He took them from bondage to freedom and accorded them much honor.
"Therefore Chazal said, 'One should be just as careful with an easy mitzvah as he is with a difficult mitzvah' (Avos 2, 1) because all mitzvos are beloved and to be cherished, since every time one performs a mitzvah he is acknowledging Hashem. And the purpose of all mitzvos is that we believe in our G-d and thank Him for creating us. This is the purpose of the entire creation, because we know no other purpose in the creation of man other than this."