REM, or short for REMARK, is used in SQL*Plus to indicate the beginning of a comment in a SQL script. Read more about REM in the documentation here.
Instead of
REM INSERTING into TABLE_NAME
I suggest you use PROMPT
PROMPT INSERTING into TABLE_NAME
That way the script output would contain the string “INSERTING into TABLE_NAME”.
More about PROMPT here. It’s especially useful when you have ECHO OFF.