Focusing on the protagonist, Gabriel, the first theme delineated is that of self-esteem or self-consciousness. Gabriel is overly concerned with the reactions of others. He recoils from his aunt's criticisms, and hesitates to make romantic overtures because he fears the reaction.
This relates to the second theme, the theme of a full life. Gabriel is stuck, or paralyzed, by his self-consciousness. He is absorbed with his concerns and does not see the world around him. He is not living fully. Consider the title, and the many mentions of dead friends and lovers throughout the story. Joyce's message is to step forward and allow oneself to grow, to mature, and to experience life.
Which carries over to the third theme, Joyce's message about his own home country. This is an Ireland, and a Dublin, stuck in a rut. The majority of the people in the city want home rule, but none of their attempts to bring it about have succeeded. They have tried and failed for 100 and more years, and never so vehemetly or with such hope as at the turning of the century. But still, they are under British rule. The people are paralyzed by a desire they can not fulfill, and the city is stuck in the middle. It must either be more assimilated into British life, or it must revolt and throw off the rule and the culture of the invading force. But, like Gabriel, its stuck in a position of indecision.