Resistances are important for mitigating damage. On Normal they certainly help but they aren’t what you would call “paramount”. You can get by without absolutely needing them, in most scenarios anyway.
What you probably read about actually was RR, or resistance reduction, which IS important on higher difficulties and can increase your damage output.
In both cases these are things you don’t need to worry about at such an early stage. Still, it doesn’t hurt to improve your resistances. Worry about RR later tho.
If you wish to learn about the games deeper mechanics then I would advise downloading the pdf guide that Nery put together here: Mechanics Guide