basic question on vim scripting

I'm playing a bit with a vim script, and I'm stuck on this problem:

if exists('b:current_line')
echom "normal! ".b:current_line."G"
exe "normal! ".b:current_line."G"
echom 'line is '.line('.')
endif

If I run the script and then do :messages, the output is this one:

normal! 6G
line is 1

and I can't understand why the cursor doesn't move... (I'm not even sure this is the correct way to move, as google isn't helping me much)

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