The line is about Gatsby's obsession. Gatsby had become consumed with the idea that he could one day win Daisy. Gatsby had met Daisy some five years earlier and fell completely in love with her, but Daisy decided to marry Tom Buchanan, who had much more money than he. Gatsby believed that if he could be wealthy too, Daisy would be within his grasp. He amasses a fortune much larger than Tom's, chiefly by means of underworld activities. Gatsby erroneously belives that Dasiy will leave Tom and marry him instead.
Nick makes this comment as he watches Daisy and Gatsby in their long awaited reunion. The rest of the line reads, "He had thrown himself into it with a creative passion, adding to it all the time, decking it out with every bright feather that drifted his way. No amount of fire or freshness can challenge what a man will store up in his ghostly heart." The ornateness of the home, the lavish parties, everything shows a man obsessed and unwilling to acknowledge Daisy's considerable flaws or the fact that she will never love him as he wants to be loved, no matter what he does or does not do.