What is a summary of the essay "Valentine's Day"? How can I analyze it?

As the title suggests, this essay is a rumination on Valentine's Day. Lamb, through his persona Elia, opens by differentiating between the St. Valentine for whom Valentine's Day is named and other, more forbidding church fathers. Lamb says there is no one who can compare to St. Valentine. He is the only one who "comes attended with ... ten thousands of little loves." What other church father, asks Elia, is accompanied by anything as charming as cupids and their flying arrows?

Then Elia anticipates the many, many Valentines the postman will deliver and wonders why the heart has become the symbol of love and the symbol of this day. Why not the liver, he asks whimsically, or the midriff?

In the next paragraph, he notes that people are always interested in a knock at the door, though sometimes what the knock brings is not welcome. But a Valentine, Elia says, is always welcome. 

Finally, Elia moves into the story of his friend "E.B." who was, according to literary critic George Wauchope, Edward Francis Burney, a painter and illustrator. E.B. watches a beautiful young woman from his window, unseen by her, and decides to send her a Valentine. He makes her an extraordinary one, filled with illustrations of famous lovers. EB watches as she receives it. She claps her hands and dances about in joy. She wasn't overjoyed because the Valentine was from her lover, as she had no lover (at least none who could draw this way), but because of the lovely images. As Elia writes:

It was more like some fairy present; a God-send, as our familiarly pious ancestors termed a benefit received, where the benefactor was unknown. It would do her no harm. It would do her good for ever after. It is good to love the unknown. I only give this as a specimen of E. B. and his modest way of doing a concealed kindness. 

While Lamb opens the essay with language that is archaic (old-fashioned, even for the 1820s) and allusive (making references to myths, religion and works of literature), by the next-to-last paragraph, quoted above, he is writing in sweet and simple terms to offer a heartfelt message. His purpose is, first, to offer a lighthearted celebration of Valentine's Day as a whimsical but delightful holiday, delightful because it spreads love. Then he becomes more serious (writing, of course, as Elia), and his moral is that doing a kind act to bring joy to a person who would not expect it is no small thing. It can be a "godsend," and an act of grace to send a beautiful Valentine to an unsuspecting person. Elia thus encourages us all to value and perform what today we might call random acts of kindness.