Source of 7 days or 3 days celebration for married couples

Question

I read in the Art Scroll Ashkenaz siddur in the section about when to omit Tachanun, that one of the occurrences is when a new groom is present in the synagogue and he is considered a "groom" from the day of the wedding (implying that this occurs even before the wedding itself if it is later in the day) and until the conclusion of the 7th day afterwards. Then, the siddur adds that if both the bride and groom have been previously married, then, for purposes of tachanun, this lasts only 3 days.

What is the source of having the celebration last 7 days? Is it related to the 7 days of creation in some way? And why is it only 3 days if both the bride and groom have been previously married?

Note I am stating tachanun merely to cite a source for where I got this info. My question is not related to the rules of tachanun

Answer 1

See the Gemara Kesuvos for the source for 7 days for virgin and less than that for previously married woman (7a-7b):

אלא הא דתניא שקדו חכמים על תקנת בנות ישראל שיהא שמח עמה ג' ימים

מיתיבי מברכין לבתולה שבעה ולאלמנה יום אחד מאי לאו אפילו אלמנה שנשאת לבחור לא לאלמון אבל לבחור מאי שבעה אי הכי ליתני מברכין לבתולה שבעה ולאלמנה שנשאת לבחור שבעה ולאלמנה יום אחד מילתא פסיקתא קתני דליכא בתולה דבצרה משבעה וליכא אלמנה דבצרה מיום אחד

Chazal instituted that a man should rejoice with his wife for 3 days.

See the Rambam (אישות י:יב):

וכן תקנו חכמים שכל הנושא בתולה יהיה שמח עמה שבעת ימים. אינו עוסק במלאכתו ולא נושא ונותן בשוק אלא אוכל ושותה ושמח בין שהיה בחור בין שהיה אלמון. ואם היתה בעולה אין פחות מג' ימים. שתקנת חכמים היא לבנות ישראל שיהיה שמח עם הבעולה ג' ימים בין בחור בין אלמון:

The Rabbis instituted that man who marries a virgin shall rejoice with her for seven days, and this he will not take part in his work and will not be involved in commerce. Rather he will eat and drink and rejoice, whether he be a new groomsman or have been a widower. And if he has married a non virgin he shall not rejoice less than three days, for the Rabbis instituted for the daughters of Israel that he shall rejoice with her for three days, whether he be a new groomsman or a widower.

The Ran on the Ri"f in Kesuvos (2a) explains the difference between a non virgin and a virgin, is because there is more Simcha for the Chosson when his wife is a virgin. As opposed to a non virgin,even if the groom has never been previously married and it is a "new" experience for him. Nonetheless it is not the same level of Simcha as when marrying a Besula.

However there are Rishonim (Ran on the Ri"f 2b, the Rashba 7a) that argue on this Rambam and holds that if if the groom had not been previously married, even though the woman was previously married and thus is not a virgin, seven days are observed. They explain that deciding factor in determining seven or three days is the level of joy of the Chosson, for that is what generates the Brachos. And since this is new to him, its level of joy is not any less than that of marrying a virgin.

Regarding as to why seven days see the Rambam (אבל א-א):

ומשה רבינו תקן להם לישראל שבעת ימי אבלות ושבעת ימי המשתה

Moshe Rabbeinu instituted for Klal Yisroel seven days of mourning and seven days of rejoicing (ie. Sheva Brachos)

The Radvaz explains the Rambam:

שיהיו ימי האבל כימי השמחה כלומר בימי המשתה יתן אל לבו יום המות וכן אמר שלמה ביום טובה היה בטוב וביום רעה ראה.

The days of mourning should be like the days of joy, meaning to say that during the days of rejoicing one should think of the day of death. As Shlomo Hamelech says "Be pleased when things go well, but in a time of misfortune reflect"

The commonality of seven days from mourning and marriage is supposed to remind us of the day of death, for us to reflect on our lives.