Yes, I don't understand the atheist's objection either. But he may be missing some of the distinctions. And possibly the argument could benefit from some clarification(?).
Every natural, innate desire in us corresponds to some real object that can satisfy that desire.
First, it's every natural, innate desire -- those are the universal desires of human nature.
This premise is saying that human beings have natural desires.
I wonder if I'm re-wording this correctly now ...
Every natural desire of a human being corresponds with something which provides *some *fulfillment of the desire.
Some natural desires would be happiness, accomplishment, justice, fulfillment, success, goodness, honor, achievement, love, distinction, discovery, knowledge, goodness, friendship, community ...
Now, all natural human desires correspond with some real object. So, any of those desires listed correspond with various natural things (including actions).
The problem may be the premise claims that these objects "satisfy" the desire.
What I am adding is the qualifiers: "fully" or "partially" (or "temporarily')
So, every desire corresponds with an object that *temporarily *satisfies that desire.
Now, the third point may be clearer:
But there exists in us a desire which nothing in time, nothing on earth, no creature can satisfy.
If we add "fully satisfy" ... this might make it clearer.
We have natural desires
Every natural desire corresponds with an object that can partially, imperfectly or temporarily satisfy that desire
But there exists in us desires which nothing in time, on earth or any creature can satisfy.
None of these desires which can be partially satisfied, can be fully satisfied in time, on earth or by any creature.
We continue to have these natural desires and they do not disappear or become fulfilled or satisfied.
This is true of all human history -- for every human being.
These natural human desires are never fully satisfied. They are also universal.
I think the argument can be filled out quite a lot more.
It's a very strong argument against materialism -- and certainly a point that is difficult to explain in evolutionary terms, for example. Where did these desires come from and why are they universal and why are they never fully satisfied? Shouldn't we know by now not to desire these things which are always frustrated and never fulfilled?