I assume your original post is directed at the theology of Universalism, the doctrine that in the end, all are saved. A critique of Universalism by orthodox Christianity is that then there's no motivation for good behavior, e.g., why not just go around "sinning" because everyone goes to heaven anyway?
Is that what you're asking?
Well, you're going into theological territory that was very well debated in the last few hundred years, involving issues like "predestination", "justification by faith", and "justification by works".
The best argument I know about this stands the original premise on its head: if you're predestined to go to hell, and according to some scriptural interpretations most are, why not go around sinning because most of us are going to hell anyway? Or, if you're behaving well just to get a reward, do you really have free will since it's the rewards that shape your behavior?
This whole line of thinking is pretty foreign to most UUs, or rejected by us. 19th-century Universalists would answer your question by saying a just God would not punish a soul eternally for a finite crime; but it is our responsibility to act justly in this world in accordance with the Christian teachings so that we can get to the kingdom (either in this world by transforming it, or a possible next one) sooner rather than later.
That's a classical Universalist motivation for being a good person: to bring about the kingdom in your own life and the lives of others.
Having said that, the whole premise that most people act morally because of a fear of damnation, or a wish to be saved, isn't really part of our repertoire anymore. Personally, I don't think it was even part of original Judeo-Christian thought; it's a Greco-Roman idea that got incorporated into Christian theology as part of the price of becoming part of the Roman Empire. :sorry1: