Ah, a subtle question. First and most simply, we're told that the jeweler loves Diana. Therefore, the first association is that of love. After that, though, hearing her name reminds him that there are other things in play besides the wealth he would make from the Duchess. There are higher standards, and appearances of honor. He just can't test the pearl while thinking of her. Hearing her name makes him imagine the perfect life he might have, and imagine just how far he might rise from his humble beginnings.
She, with the beautiful exterior self, holds a strong dominance over him and this perfect quality captivates him as he say in a metaphorical flourish about the queen lavishing beauty and "goddess" look. He had already fallen in love with her and that "grand entrance" of hers gave light to his golden future and he knows he won't be despised by his low and humble beings and somebody do care for him. It brings a bright spark to his empty life and make him come out from his inner demons.