My translation (not the best): "and dark Care [Cura] sits after the member of the equestrian order. But if [quodsi] neither the clearer Phrygian stone [lapis; a type of marble] nor the use [usus] of shellfish [purpurarum; used to make crimson/purple dye, from Tyre] soothes clearer in the sky [sidere], nor the Falernian [Falerna] wine and the Persian [Achaemenium] aromatic plant [costum], why might I labor [moliar, deliberate subjunctive of molior] for the atrium with envy-causing [invidendis] door-posts [postibus] and the new sublime style [ritu; from ritus]? Why might I exchange [permutem, from permutare] the Sabine valley for the toilsome [operosiores; epic word] riches [divitias]?"

I think this poem is about longing for a simpler life, and money, luxuries, etc., isn't everything. I suppose the equestrians, the closest Rome ever got to anything remotely comparable to our middle class, would have been anxious about wealth, rather like some members of the middle class are today. The Romans valued austerity, hard work, frugality and discipline (like Americans traditionally did); this is Horace's way of calling for a move away from the "greed is good" era of Rome. However, Horace's estate was rather nice (though of course he's quick to point out that his was a gift from Maecenas), so how seriously should we take him?

I got the ablative and nominative (atra Cura) confused! The diction and synax wasn't too horrible, like many Horacian poems.