12 zodiac signs,
12 tribes of Israel,
12 months (ok I know about the caesar calender thing)
12 hours in a clock face (i wrote 'on a clock face'. I know there are roughly 24hrs in a day)
12 disciples of Jesus (possible that the writers of the bible choose it to be the number of the followers since it was already special?)

Now abt 7 -
7 MAIN colours in a rainbow (note that i used main- Vibgyour)
7 days in a week
7 is considered to be a lucky number

k.k I know that the bible and astrological folks (religion could be based largely on astrology) consider these numbers to signify 'completeness' but there has to be a reason for it. U can't just take a number and consider it lucky for nothing right?

One more thing - besides having a 'spiritual or astrological significance' do these numbers also have a numerological or MATHEMATICAL or SCIENTIFIC significance?