What is the difference between Main Idea and Theme?

Read the excerpt from queen elizabeth's response to parliament's request that she marry. for i assure you (what credit my assurance may have with you, i cannot tell, but what credit it shall deserve to have, the sequel shall declare) i will never in that matter conclude any thing that shall be prejudicial to the realm. for the weal, good and safety whereof, i will never shun to spend my life; and whomsoever it shall be my chance to light upon, i trust he shall be such, as shall be as careful for the realm as you; i will not say as myself, because i cannot so certainly determine of any other, but by my desire he shall be such as shall be as careful for the preservation of the realm and you, as myself. in this excerpt, queen elizabeth says "for the weal, good and safety whereof, i will never shun to spend my life" in order to convince her audience that she is unbiased, intelligent, and rarely makes mistakes. inform her audience that she will work hard to win back the broken trust of her followers. persuade her audience that she will never make personal decisions that will harm england. remind her audience that she is the ruler and in charge of enacting laws that protect england.

Read this excerpt from the lady of shalott by alfred, lord tennyson. in which three lines does the poet reveal the monotomy of the lady’s existence

In at least two hundred words, discuss why "désirée's baby" is or is not relevant today.