Hi Kaybear.
The bible itself has a story to explain why the number seven is used so much;
Genesis 21:24-31
The punch line is verse 31 --
Genesis 21:31 Wherefore he called that place Beer-sheba; because there they sware both of them.
In Hebrew the word for seven is "sheba"; and that exact same word means a promise or oath.
Also in Hebrew the word for "well" is "beer" (funny, except for the well in Cana, no water is wine or beer.... but that's one of those odd coincidences?)
So, anyway, Beer-Sheba is the "7 well" or the "well of oath".
The other poster above is also correct, for an Oath means not luke warm; therefore it also means "fullness", "completely", "truthfully".
A man who has seven demons, effectively (in Jewish idiom) has them "all"!
And again...
When God promised to avenge Cain if someone killed him in revenge for Abel; He gave Cain the mark "7".
And when Cain's son, Lamech, killed two people (possibly 1 by mistake, and 1 in defense ) he said:
Genesis 4:24 (although some bibles say 77 times, in Greek its 7x70 times )
That happens to be the number 7x70 mentioned in Matthew 18:22 for forgiveness; which makes me think God might have forgiven Lamech.
But, at the same time -- it's not a literal 490 forgive-nesses and then "strike out";
For the numbers about a promise, and in Matthew 18:23-35 ; You can see that failing even ONCE to be merciful to ANOTHER (besides the one who forgave you) can be enough to suspend the mercy of a free promise. ( Not that God can't be merciful again in the future.)
Our Father, who art in Heaven, holy is your name.... forgive us our trespasses as we forgive those who sin against us.
Glad to have you here on the forums.
I hope you find what you are looking for; and that you keep what is good -- and learn to discard what is not; as all forums have all kinds of people.
And I hope I haven't answered your question more than you ever wanted to know about the number 7 -- but hey, I can only guess at what beautiful mind is on the other side of the screen...