It's just like you had cast the spell. That the copy didn't exist before you activated the Sceptor doesn't matter. If you had played a land, then cast Demonic Tutor for Rest for the Weary, then Rest for the Weary, it'd be the same even though the land play was practically ages ago at that point. The only thing that matters is, it happened this turn.
Check the Gatherer page here, it quotes the Oracle at the bottom there, answering many similar questions.
July 11, 2016 4:39 p.m.
A card does what it says, no more and no less. The copy of Rest for the Weary made by Isochron Scepter's ability is an exact copy of the original. If a land entered the battlefield this turn then it will give you 8 life when you cast it.