Without death: assuming we’re talking about humans, and this happens as a result of human intervention….
Well, for one thing, the population would grow. There might be a tendency to have fewer children. I don’t think it’s fair to say resources are limitless, since that doesn’t lead to much of a thought experiment. I think people would have to still work to find more resources.
Resources would accumulate amongst the old. There would be no transfer of wealth from the old to their children, so there would be no inheritances. Of course, parents could always gift things to their children. However, I think there would be tensions that develop between the oldest old and those who are younger.
Of course, all the implications I suggest could potentially be seen as causes of pain. You do not specify if you are only talking about physical pain. Although, even if you are, I don’t think you can separate emotional pain and distress from physical pain.
I think that struggle motivates us. If we had no struggle, we’d end up doing next to nothing. Why would we have to? I mean, with no pain, we’d have no boredom, so we wouldn’t have to find things to interest us. I think we’d end up as @mattbrowne said: as very large lumps of organic matter. Our brains would atrophy, since we wouldn’t need them to survive. We wouldn’t need muscles or anything else. We’d probably end up as lumps of protoplasm. We’d have no children, and little of anything else.
I think without things to struggle against (such as pain), we would have little or no advancement. There would be no point in it. There would be no point in thinking. I think it is struggle and death that push us to fight pain and death, and that is what makes us cleverer and cleverer about ways to reduce pain and push off death.
We may not like pain, but that is exactly why we need it. I’d hesitate to say we need death, because I don’t like the idea of dying. However, I think that the possibility of fending off death does motivate us. Death needs to exist, but it doesn’t have to happen to everyone in order for it to motivate us. All we need is the possibility of death if we are not careful enough, or we don’t constantly seek to improve our chances of avoiding death.
Are you thinking of suggesting the existence of such a world? I have to think that if such a world existed from the beginning of time, there would be no biological matter at all. Nothing would ever need to fight to stay alive, so it never would change. The first form of life, whatever it was, would be the only form ever to exist. I’m not even sure we would recognize it as life. There would be no need for change. The universe would be static and consciousness would never develop. Without consciousness, nothing could be said to “exist,” because there would be no entity capable of becoming aware of existence. The universe would become irrelevant. Poof!