Why can't i use same file channel twice in TCL

I was writing a TCL program which looked something like this :

#!/usr/bin/tclsh
set fInp [open file1.txt r]
while {[gets $fInp line] >= 0} {
      statement 1
      statement 2
}

statement 3
statement 4

while {[gets $fInp line] >=0} {
      statement 5
      statement 6
}

close $fInp

I was expecting this to work fine , but to my surprise , the second while loop was not getting executed at all. I came to a conclusion that we cannot read a file in TCL twice using same file descriptor (or channel)

So I closed the fInp and opened that file again using fInp2 , and it worked !

What is the reason behind this behavior , and is there any other way of doing it ?

Thanks