Why is the week seven days?

 

If Allah swt made everything in 6 days why do we have 7 days in a week?.

Praise be to Allaah.

Firstly: 

We cannot be certain about
anything with regard of the division of the week into seven days, or the
time when this division began – was it before the creation of the heavens
and the earth, or was the creation of the heavens and the earth what led to
this division? The reason for that is that we have no clear evidence which
states anything certain to that effect. But what is indicated by a study of
calendars and the customs and reports of different nations is that the
division of the week into seven days is connected to religion and taken from
it, and that it has to do with reports and rulings of religion. 

Shaykh al-Islam Ibn
Taymiyah (may Allaah have mercy on him) said in Majmoo’ al-Fataawa
(7/95): 

Every nation that does not
have a Book has no names for days of the week in their languages, rather
they have names for the day, the month and the year, because that may be
known on tangible and rational ways, so the nations gave them names, because
expression follows visualization. But the week was only known by hearing
(reports). It was not known that Allaah created the heavens and the earth
and everything in between in six days then rose over the Throne except by
the words of the Prophets who were enjoined to gather together on one day of
the week to worship Allaah and remember the first week in which Allaah began
to create the universe. In Arabic and Hebrew and the languages of those who
learned from them, there are words for the days of the week, unlike the
language of the Turks and others like them; there are no words for the days
of the week in their language because they did not know of that so they have
no words for it. 

Dr. Jawaad ‘Ali says: 

The month is divided into
four sections, and each section is a week composed of seven days. 

The idea of this division
is attributed to the Babylonians, but the days of the week and their order
in the manner that is known until now is a system that appeared long after
them. The week (shavu’ah in Hebrew) is mentioned in the Torah, in the Book
of Genesis. Based on both the Jewish Sabbath and the story of creation, the
week was organized along the lines that are still prevalent today. End
quote. 

Al-Mufassal fi Tareekh
al-‘Arab qabl al-Islam (16/96). 

And Allaah knows best.