One purpose of Tom's opening monolog is to ground the audience in the setting of the play. After brief opening remarks, he immediately establishes both time and place.
First, he tells the audience he is turning back time to the 1930s; he refers to the "dissolving economy" in America, reminding the audience it is the time of the Great Depression.
Tom then mentions revolution in Spain and alludes to Guernica, the Spanish city destroyed by German and Italian planes in the first aerial bombing of an urban population.
Each reference to the events in 1930s Spain is contrasted with simultaneous situations in this country. Very effectively, Tom communicates that the story he is about to share will unfold against a backdrop of a world caught up in profound upheaval.
Tom's summary of world events emphasizes thematically the confinement and isolation of the dingy Wingfield apartment. The world without is one of reality; the world within is one of illusion.
Tom's references to the events in Spain function in another significant way. They foreshadow the world war that soon followed the American Depression. In Tom's very moving closing monolog, he alludes to World War II when he says that Laura can blow out her candles, "for nowadays the world is lit by lightning!"
By contrasting the social backgrounds of America and Spain, Tom masterfully establishes the setting and the tone of the play and foreshadows its conclusion.
The comparison becomes very important when Tom expresses his longing for adventure. He contrasts Spain with America, telling us that in Spain things were happening, while in America all we had was jazz, liquor, and sex. He is longing to do, and says he's tired of going to movies and seeing other people have adventure. It truly expresses his frustration with life.
I also think the "lit by lightning" part just refers to the times they were in. He is telling Laura to blow out her candles, because up until then, electricity was still becoming new. Jim talks about wanting to go into television, and Tom is telling Laura to move forward because the world is changing.
This show can touch so many people on so many different levels, going back over it, one will never get the same answer twice for why things are in the play.