Genesis 7:10: “And it came to pass after the seven days that the waters of the flood were upon the earth.”
Sanhedrin 108B: “And it came to pass after the seven days… What was the purpose of these 7 days? The Holy One Blesses is He gave them a taste of the world to come.”
Torah Temimah Colloquial Translation on Note #7
The toseftah for tractate Sotah (chapter 10) explains this more clearly as follows: “The Holy One Blessed is He gave them 7 days of eating and drinking in order that they should realize what they lost.” Yet, the reason for this benefit is not explained. Perhaps one could explain this based on the Gemara Taanit 21A
The men on watch in the temple did not fast on Sunday so as not to go from rest and pleasure to fasting and pain.
The commentators explain that trouble that comes after pleasure is harder than trouble that comes in an expected time. Therefore, Hashem gave the generation of the flood a period of great pleasure before the flood to that their pain be greater as they perished in the flood.
In another place we explained, based on this, the reason, as we hold, that anyone who eats and drinks on the 9th (of Tishrei), the day before Yom Kippur, it is considered that the person fasted on the 9th and 10th. At first glance this merit is perplexing how can it be that eating and drinking can be counted as fasting? As explained, that a fast that comes after a period of much eating is harder, the increase of eating drinking on the 9th is a preparation for greater affliction on the 10th. Thus it is considered as if one fasted two days. Take note.
As to why Hashem decided seven days for this, one must say that it is revealed to Hashem that it takes seven days for a person to be fully satiated. Since Hashem wanted to satiate the generation of the flood up to the last minute, as explained, He therefore decided on these seven days. According to this, one can say this is the reason for the seven days of feasting for rejoicing newlyweds. Since it is a mitzvah to cheer up the bride and groom as much as possible, they established seven days to ensure maximum joy. This is also the reason for the seven days of a festival , on which, one must have extra rejoicing. One can also associate with this the seven days of mourning as it is written: “And I will turn your feasts into mourning …” See also Judges 14:17. We see that the two are juxtaposed. Just as a person will not be fully satisfied until seven days, so too, mourning will not dissipate in less than seven days. Take note. No further explanation is necessary.
One must clarify what is stated in Bava Basra 17a “The Holy One Blesses is He gave three people a taste of the world to come: Abraham, Isaac and Jacob.” Yet, our Midrash states that Hashem also gave the generation of the flood a taste of the world to come. One must say that even though the language is similar the intent is different. Hashem gave the forefathers a taste of the world to come so they would know what they would merit. Thus their pleasure in this world was like the pleasure of the world to come. Not so for the generation of the flood. The Midrash does not mean that the Holy One Blessed is He gave them a hint of the pleasure of the world to come. Certainly, because of the evil ways, they did not believe in the world to come. Nor, did they get a portion thereof as the Gemara explains. He only satiated them with all the pleasures [of this world] as numerous as the pleasures of the world to come. This Midrash describes to us (who understand the pleasure of the world to come) the value and measure of pleasure, with which, He satiated the generation of the flood. They, however, did not understand this; filling themselves with the pleasures of this world so much, that, at the time of their destruction, they would long for those pleasures.
Editor’s note: I find it very interesting how the Torah Temimah extends the ides of the seven days to other areas of Halacha. We should take to heart that our focus should not be on this world, but on the pleasure we can merit in the world to come
 Yoma 81b
 E.g. Passover or Succoth
 Amos 8:10
 And she wept before him the seven days, while their feast lasted; and it came to pass on the seventh day, that he told her, because she pressed him sore; and she told the riddle to the children of her people