Well, I saw on internet to just steal stuff from the church and use on him.

PRoblem 1: I am paladin, and I wish I did not had to steal stuff.

Problem 2: I stole it anyway because it was the only thing I figured, but when I used the yellow potion the godamned retarded managed to pull a saving throw (he rolled 16 :/) and I cannot figure how to use scrolls at all O.o (also how I identify potions and scrolls, all of them are just "magic potion" and "magic scroll")

You need to use the "read magic" spell, or else pay 100 gold (!!!) per item to have a merchant identify them. Scrolls must be identified before they are cast, but you can activate potions blindly. Hope you have a wizard or cleric in the party.

You cannot get the items needed without stealing from the temple?

That sounds so silly :/

Most of the fetch quests in Hommlet are.

Technically any Cleric high enough level to cast the "heal" spell doesn't need the scroll, but you're basically going to be at the end-game by the time that's the case. The craziest thing is that the scroll is worth about 1500 GP! It's one of the most valuable things in Hommlet, just sitting around on a shelf where anyone can go and grab it.

Heal spells, potions and scrolls are all available later on.
Pinching the scroll from the church is just a shortcut (though an intended one).

A reason to have a less holy rogue in the party to do the stuff you can't roleplay a paladin to do. :)