Does anything really matter?
Nothing matters unless there's somebody it matters to. Imagine if there were no sentient beings in the universe--neither human, alien, nor spirit. There is only matter and energy. In a universe like that, all kinds of things may be going on. Stars nova, commets smash into planets, and galaxies are formed. But none of it matters if there's nobody it matters to. It doesn't even matter whether anything is happening at all. It doesn't matter whether the universe even exists or not. Since it doesn't matter, there is no particular way things ought to be. "Ought" applies to nothing at all in a universe like that. So there is neither right nor wrong, good nor evil. Things just are.
Now consider the human condition. Here we are on a tiny spec of dust in the universe called "Earth," having recently come to the realization that in a few billion years, the Sun is going to begin to expand until all life on earth is destroyed. Assuming by that time we haven't figured out how to set up colonies on other planets in other solar systems, humans will cease to exist.
That raises a question: Once humans are gone, will it matter that they ever existed at all? It can only matter if there's somebody it matters to. If there's nobody it matters to, then it will not have mattered. If it doesn't matter that humans ever existed at all, then nothing humans did while they existed matters.
That raises another question: Since humans haven't ceased to exist yet, does anything matter now? Again, it only matters if there's somebody it matters to. Perhaps it matters to humans themselves. Individuals and societies pour significance into the various things that happen to people, but they don't all pour the same significance. Suppose, for example, that some nice old lady is skinned alive and left to die because some sadistic crazy person thought it might be fun to watch. One person might be outraged, but another person may not care at all. Does it matter or not?
Well, it matters to one person, but not to the other. There is no objective answer to the question, though. There is no ultimate meaning in it at all if significance depends merely on human preferences.
The only way there can be a correct answer to the question--an answer that is true whether two people agree with it or not--is if there is some sentient being who transcends humanity. This being must not only be sentient and stand over and above humanity, but this being must have some ultimacy about it. It must be some sort of necessary being, a being on which everything else depends, and therefore is invested with its meaning. Only if this being exists can anything matter in any ultimate sense. If there is no such being, then nothing ultimately matters.
If there is a necessary, sentient, and transcendent being on which everything else depends, and things matter to this being, then there can be ultimate meaning. Things like suffering and death would not just be things we either care about or don't, but they would be real tragedies whether we recognized it or not, because it would matter to the ultimate being.
Without supposing that such a being exists, we can appropriately call the being "God" since the being is necessary, sentient, trancendent, and is a being on which everything else depends for its existence and meaning. If there is no God, then nothing matters in any objective sense, because meaning is left to the subjective preferences of contingent and transient beings, like humans. If nothing matters in any objective sense, then there is no particular way things ought to be. If there's no particular way things ought to be, then there's no right or wrong, good or evil. In short, if there is no God, then there are no objective moral values.
For more on this subject, check out The Absurdity of Life Without God by William Lane Craig.