השמר לך פן תשכח את ה' אלקיך לבלתי שמר מצותיו ומשפטיו וחקתיו אשר אנכי מצוך היום.
Guard yourself, lest you forget Hashem your G‑d, and fail to observe the mitzvos, laws and statutes that I command you today.
The warning in this week’s parshah to never forget about Hashem seems redundant in light of an almost identical warning stated in last week’s parshah:
השמר לך פן תשכח את ה' אשר הוציאך מארץ מצרים מבית עבדים.
Guard yourself, lest you forget Hashem your G‑d, who liberated you from the Land of Egypt, from the house of slavery.
Why did Moshe Rabbeinu find it necessary to twice caution us never to forget Hashem? Upon deeper contemplation, we see that these two verses highlight two distinct aspects of remembrance. In last week’s parshah, we are warned to remain mindful of Hashem’s presence, as David HaMelech said: שויתי ה' לנגדי תמיד – “I have placed [awareness of] Hashem before myself at all times.” We must recognize Hashem’s constant involvement in our lives; love Him for His unending kindness; revere Him for His awesome greatness; and constantly bless and thank Him for all that he has done for us as individuals and as a nation, most particularly for liberating us from slavery. Contemplation of the blessings we enjoy in our lives should engender a heightened awareness of Him Who granted them, as is evident from the context of the verse in last week’s parshah:
והיה כי יביאך ה' אלקיך אל הארץ אשר נשבע לאבתיך לאברהם ליצחק וליעקב לתת לך ערים גדלת וטבת אשר לא בנית. ובתים מלאים כל טוב אשר לא מלאת וברת חצובים אשר לא חצבת כרמים וזיתים אשר לא נטעת ואכלת ושבעת. השמר לך פן תשכח את יקוק אשר הוציאך מארץ מצרים מבית עבדים.
And it will be, when Hashem your G‑d will bring you to the Land that He swore to your forefathers, Avraham, Yitzchak and Yaakov, to give unto them – large and good cities that you did not labor to build; houses filled with everything good that you did not labor to fill; cisterns that you did not labor to dig; vineyards and olive orchards that you did not labor to plant – and you will eat and be satisfied. Guard yourself, lest you forget Hashem your G‑d, who liberated you from the Land of Egypt, from the house of slavery. 
In this week’s parshah, this warning is expanded to remind us of the obligations that our debt of gratitude incurs. Therefore, the verse in this week’s parshah stresses the remembrance of Hashem in the context of His Torah and mitzvos: “Guard yourself, lest you forget Hashem your G‑d and fail to observe the mitzvos, laws and statutes that I command you today.”
Thus, these two warnings stress two different aspects of remembrance. Firstly, we must remember to remain aware of Hashem. Secondly, we must remember to show Him the gratitude He deserves by lovingly and obediently fulfilling His mitzvos.
A parallel to this can be found in the mitzva to remember the Exodus from Egypt, which is also a twofold obligation. Firstly, we must recognize Hashem’s kindness in liberating us from slavery; and secondly, we must accept upon ourselves the debt of gratitude that this entails, by fulfilling His commandments, as we learn from the possuk, בעבור זה עשה ה' לי בצאתי מארץ מצרים – “For the sake of these (mitzvos), Hashem performed for me miracles when I left the Land of Egypt.”
The obligation to serve Hashem in appreciation of His having redeemed us is a central theme of the Seder and perhaps the most important lesson of the Exodus. Therefore, this verse is repeated three times in the Pesach Haggadah. It is the answer to the wicked son, who asks, “What is this service to you?” It is the answer to the son who does not know how to ask. And it is the source from which we learn that the story of the Exodus must be retold on Seder Night, when matza and maror are set before us.
There is a mitzva to recall the Exodus every morning and night. From the many verses discussing the Exodus, any of which would fulfill this obligation, our Sages chose the verse, אני ה' אלוקיכם אשר הוצאתי אתכם מארץ מצרים להיות לכם לאלוקים - ”I am Hashem, you G‑d, Who took you out of Egypt to be your G‑d,” which we recite twice each day in Krias Shema. This verse highlights the central message of the Exodus: the debt of gratitude it places upon us and obligates us to accept Hashem’s Kingship.
Each of the four sons responds to the story of the Exodus in his own way. However, only the wise son discerns its true message and asks the paramount question of the evening: “What are the testimonies, the decrees and the rulings that Hashem, our G‑d, has commanded you?” In other words, “What does the remembrance of Hashem’s miracles require of us, to properly show our appreciation?”
The wicked son also understands that the Exodus is more than just a story. It is a claim on our sense of gratitude. But rather than honor this debt, as the wise son does, he utterly and insolently rejects it, saying, “What is this service to you?” – “To you,” he says, but not to himself, since he refuses to honor our debt of gratitude. “What are these difficult burdens of religious observance that you impose upon me throughout the year?” states the Talmud Yerushalmi in explanation of the wicked son’s question.
The only appropriate response to his question is the verse stated in the Haggadah, “For the sake of these (mitzvos), Hashem performed for me miracles.” For me, but not for him. Had he been there, he would not have been redeemed, since the whole purpose of our Redemption from Egypt was so that we may serve Hashem, as the Midrash states, “I liberated them from Egypt, in order that they may serve Me.” By rejecting this debt of gratitude, the wicked son rejects the entire premise of the Redemption.
For the son who does not know how to ask, we need not enter into deep philosophical dissertations or Talmudic extrapolations which are beyond his ability to understand. We need only point to the matzos and maror, the mitzvos of the night, and tell him, “For the sake of these mitzvos.” Suffice it for him to grasp the central point of the night, namely that our debt of gratitude to Hashem obligates us to fulfill His mitzvos.
The verse states, כי לי בני ישראל עבדים, עבדי הם אשר הוצאתי אותם מארץ מצרים - “For Bnei Yisrael are My servants. They are My servants, whom I liberated from the Land of Egypt.” The Midrash comments on this possuk, explaining: “I liberated them from Egypt in order that they may serve Me.” Upon contemplating the miracles of Redemption and the hidden miracles that constantly surround us, let us be inspired to redouble our efforts in the service of our Merciful King, who loves us, cares for us, and constantly provides our needs.
 Devarim 8:11
 Devarim 6:12
 Tehillim 16:8
 Devarim 6:10-12
 Shemos 13:8
 Shemos 12:26
 Devarim 16:3; Berachos 12b
 Bamidbar 15:41
 Devarim 6:20
 Shemos 12:26
 Talmud Yerushalmi, Pesachim 70
 Vayikra 25:55