[Radek]

It's a problem of high level spells. You need a level 6 (7) priest to get level 6 (7) priest spells. You can also become a level 6 (7) paladin and ranger with the same effect later.
Which spells? I recommend Rebirth and Exorcism (level 7 Spirit spells), Restore Health and Dust to Dust (level 6 Spirit spells) and Cure (level 6 Vine spell) at least. Also, if you plan the Blessings skill for your priest then you will appreciate Artifact of Spirit (level 7 Spirit spell).
Not all these spells are needed right now. Only the Cure spell is urgent. You will find Exorcism and Restore Health helpful in Brimloch Roon but Brimloch Roon is far away and you can live without these spells in the end. The Dust to Dust spell is a splendid tool against dangerous undeads with bags of HPs but you can kill these undeads with your weapons, too. The Artifact of Spirit makes sense only if your priest will bless items. Otherwise, do not teach the priest the spell.