What does Antonio mean when he says, "I hold the world but as the world, Gratiano"?

This quotation comes in Act I Scene 1.  In his first line, Antonio declares to Salarino and Salanio, “In sooth, I know not why I am so sad:/It wearies me.”  His two companions attempt to help him isolate the source of his sadness – he is sad because he is not at sea; he is sad perhaps because he has not had success with his merchandise; maybe because he is in love; it could be...

This quotation comes in Act I Scene 1.  In his first line, Antonio declares to Salarino and Salanio, “In sooth, I know not why I am so sad:/It wearies me.”  His two companions attempt to help him isolate the source of his sadness – he is sad because he is not at sea; he is sad perhaps because he has not had success with his merchandise; maybe because he is in love; it could be that he feels sad simply because he is not happy, or it could simply be his disposition.  Antonio discards each of these suggestions in turn.  After this exchange, Salarino and Salanio leave the stage while Bassanio appears on the scene with Lorenzo and Gratiano.  Gratiano immediately comments on Antonio’s unhappy visage:  “You look not well, Signior Antonio;/You have too much respect upon the world:/They lose it that do buy it with much care.” 

Here Gratiano is saying that Antonio’s problem comes because he cares too much of the world’s opinion, and anyone who spends his life worried about what others think of him will lose their respect.  Antonio denies this statement when he says “I hold the world but as the world” – he does not care any more than he should about the world’s opinion.  He holds no one and nothing to any greater esteem than that to which it ought to be held.  It is simply “A stage where every man much play a part,/And mine a sad one.”  And thus he discards another suggestion for why he could be sad.

Even though with this line Antonio denies caring about public opinion, Gratiano is not convinced and goes on a bit of a rant against his friend’s sulking, finishing with the warning:  “fish not, with this melancholy bait,/For this fool gudgeon, this opinion.”  Though Antonio denies it, he will not be convinced.  And, comically, after Gratiano and Lorenzo have left the scene, Bassiano confides to Antonio that “Gratiano speaks an infinite deal of nothing.”