The þainneið is an oath which, in the properly witnessed taking, makes the taker a thane of Thule if they were eligible for that office. Here is its text, in Thulic; here is a translation into IF Common:

I take as my charge this country and its people, and I swear none shall go hungry that my hand can feed, and none shall be killed that my hand can protect. With this oath I become a thane of Thule, servant to its ruler and friend to its people. May I never forget my duty.