Different frames of reference
I think the case here is of different frames of reference. The older generation had known the former temple in all its glory and therefore could not help but be reminded of how low they had gone. They were comparing their present situation to a much better one, and therefore could not be completely happy as they knew God was capable of more. Those, however, who'd never seen any better, had a much smaller frame of reference and therefore felt happy with the little they'd accomplished. This also happens in life. When you get used to something bad, you become happy with just anything. But when your standards are higher, you always fight for something better and are not satisfied until you get it.
Created over 3 years ago