(י) וְאָכַלְתָּ֖ וְשָׂבָ֑עְתָּ וּבֵֽרַכְתָּ֙ אֶת־יְהֹוָ֣ה אֱלֹהֶ֔יךָ עַל־הָאָ֥רֶץ הַטֹּבָ֖ה אֲשֶׁ֥ר נָֽתַן־לָֽךְ׃
(10) When you have eaten your fill, give thanks to the LORD your God for the good land which He has given you.

Adam: Always be sure to say grace after a meal to not be ungrateful to God since He is the one blessed us with the food.

Jackson: Food is like books. There are many varieties of books like there is of food. Just like you have food in your home, librarians have books at the library. We have to be thankful that the books are there for out education and entertainment. So too, God had the thought of the food before we had the food, like the authors do for books.

(א) בָּרוּךְ אַתָּה יְהֹוָה אֱלֹהֵינוּ מֶלֶךְ הָעוֹלָם הַזָּן אֶת הָעוֹלָם כֻּלּוֹ בְּטוּבוֹ בְּחֵן בְּחֶסֶד וּבְרַחֲמִים, הוּא נֹתֵן לֶחֶם לְכָל־בָּשָׂר כִּי לְעוֹלָם חַסְדּוֹ וּבְטוּבוֹ הַגָּדוֹל תָּמִיד לֹא חָסַר לָנוּ וְאַל יֶחְסַר לָנוּ מָזוֹן (תָּמִיד) לְעוֹלָם וָעֶד בַּעֲבוּר שְׁמוֹ הַגָּדוֹל כִּי הוּא אֵל זָן וּמְפַרְנֵס לַכֹּל וּמֵטִיב לַכֹּל וּמֵכִין מָזוֹן לְכָל־בְּרִיּוֹתָיו אֲשֶׁר בָּרָא בָּרוּךְ אַתָּה יְיָ הַזָּן אֶת הַכֹּל.

(1) Blessed art You, Adonai our G-d, Ruler of the universe, who feeds the whole world with Your goodness, with grace, with loving kindness and tender mercy; You give food to all flesh, for Your loving kindness endures forever. Through Your great goodness, food has never failed us: Oh. may it not fail us forever and ever for Your great name's sake, since You nourish and sustain all beings and do good unto all, and provide food for all ofYour creatures whom You have created. Blessed are You, Adonai, who gives food to all.

From Tractate Zeraim in the Jerusalem Talmud: In addition to the blessings to be recited before eating, the tractate discusses the blessing ordained in the Torah (Deut 8:8), known as Birkat Hamazon ("the Grace after Meals"), to be recited after eating food; while the Torah obligation applies only to a meal that satisfies a person's hunger, the rabbis of the Mishna required that it be recited after eating a k'zayit measure (an olive bulk) of bread. When three or more men have eaten together, one of them is required to invite the others to recite the Grace after Meals in what is known as the zimmun ("invitation to bless") (Wikipedia)

From AlephBeta:

The Meaning of Birkat Hamazon: Why We Pray After Meals

Jewish law commands us to make a short blessing on food items before we eat them. In addition to this, the Torah also commands us to make a blessing after we eat. It may seem excessive to say Grace twice, but this additional blessing after meals is actually very significant.

After we’ve eaten and are no longer hungry, our inclination may be to run on to the next thing without giving a second thought to the meal we just finished. However, the seemingly mundane act of eating is an incredible testament to God’s kindness; we are only able to satisfy our hunger because God designed a world which provides us with nourishing food. Saying Grace forces us to take a few minutes after every meal to recognize this, and show our appreciation for God’s blessings and care.

Our Sages take this idea a step further by explaining that the Grace After Meals is not just about being thankful, but about being humble. After feasting on a good meal, we feel full and satisfied. This contentment can easily cause us to become overly confident in our place in the world, and to relish in the power of being top of the food chain. When we are most at risk of forgetting God’s dominion over us, saying Grace After Meals reminds us of this important and fundamental religious principle.

Miya: When you eat a meal you have to think about where the food came from and not just who made it for you. And that is why you say Birkat after you eat food because God has given you the food and the land so that you can appreciate where it came from

Micah: after eating you sometimes go straight back to your room to finish what you were doing, but there are many people in the world who don't know when they will be able to eat again. You want to be more thankful in life because you are very fortunate in life to be able to eat like that