That looks more complex than is needed, which is maybe not helping. I am making a few assumptions based on your previous requirements, etc.
Now, the outer loop:
That is reading 12 values per line from a file, yes? If so, then the next loop:
while read a b c
does nothing more than assign the value you already have ($a and) to a different variable ($line) and is, thus, really not needed!
for line in $a
The inner loop
will iterate over the 3rd to 12th columns of the line of the file.
for i in $c
What you seem to be doing is finding a list of files that contain the value of the first column of your driving file ($a) and then renaming the found files.
A bit more detail (an example couple of lines from the file) will be of help here.
The moon on the one hand, the dawn on the other:
The moon is my sister, the dawn is my brother.
The moon on my left and the dawn on my right.
My brother, good morning: my sister, good night.
-- Hilaire Belloc