why did judith slays holofernes
The episode of Judith beheading Holofernes is from a deuterocanonical book of the Bible. The episode is from the apocryphal Book of Judith in the Old Testament, which recounts the assassination of the Assyrian general Holofernes by the Israelite heroine Judith. Gentileschi draws upon the most climatic part of the Book of Judith where the beheading takes place.
She also painted a later version of the work somewhere between 1613 and 1621, now in the Uffizi in Florence.   
The daughter of painter Orazio Gentileschi, Artemisia trained in her father’s workshop and quickly earned acclaim, completing her first signed painting, a dramatic yet sensitive rendering of Susanna and the Elders, when she was just 17. Her style bears some resemblance to that of her father, who was a follower of Caravaggio, but Artemisia’s paintings stand out for their theatricality—the raw emotional intensity of a few figures daringly arranged. The younger Gentileschi’s work is also distinctive in its focus on powerful heroines, capturing both their vulnerability and strength, a feature many attribute to events in Gentileschi’s own life. At the age of 18, she was raped by one of her father’s colleagues, Agostino Tassi. He was convicted in a trial a year later after Artemisia was tortured to “confirm” her testimony, but Tassi was never punished. Within months of the conclusion of the trial, Artemisia was quickly married and moved to Florence with her new husband.
One of the most famous and skilled painters of the Baroque era, Artemisia Gentileschi was centuries ahead of her time. Among the first women artists to achieve success in the 17th century, she brought to her work an electric sense of narrative drama and a unique perspective that both celebrated and humanized strong women characters. Rediscovered by feminist art historians in the past few decades, Gentileschi has inspired a spate of books, both scholarly and popular, and a number of films. But it is the sensational painting Judith Slaying Holofernes (c. 1620) that epitomizes her career. The Art Institute of Chicago, in collaboration with the Foundation for Italian Art and Culture (FIAC), is thrilled to present this stunning work, an exceptional loan from the Uffizi Gallery in Florence, for its first display in Chicago.
Judith remained popular in the Baroque period, but around 1600, images of Judith began to take on a more violent character, “and Judith became a threatening character to artist and viewer.”  Italian painters including Caravaggio, Leonello Spada, and Bartolomeo Manfredi depicted Judith and Holofernes; and in the north, Rembrandt, Peter Paul Rubens, and Eglon van der Neer  used the story. The influential composition by Cristofano Allori (c. 1613 onwards), which exists in several versions, copied a conceit of Caravaggio’s recent David with the Head of Goliath: Holofernes’ head is a portrait of the artist, Judith is his ex-mistress, and the maid her mother.   In Artemisia Gentileschi’s painting Judith Slaying Holofernes (Naples), she demonstrates her knowledge of the Caravaggio Judith Slaying Holofernes of 1612; like Caravaggio, she chooses to show the actual moment of the killing.  A different composition in the Pitti Palace in Florence shows a more traditional scene with the head in a basket.
Two notable paintings of Judith were made by Gustav Klimt. The story was quite popular with Klimt and his contemporaries, and he painted Judith I in 1901, as a dreamy and sensual woman with open shirt. His Judith II (1909) is “less erotic and more frightening”. The two “suggest ‘a crisis of the male ego’, fears and violent fantasies all entangled with an eroticized death, which women and sexuality aroused in at least some men around the turn of the century.” 
Editors’ Tip: Artemisia Gentileschi: The Language of Painting
Among the pioneering women artists from the Baroque period there was the celebrated Italian Artemisia Gentileschi. Although she came from the established artistic family, her father being famous Tuscan painter Orazio Gentileschi, and was exposed to the traditional set of themes (historical/religious), she managed to form specific and recognizable painterly approach based on a feminist agenda.
Artemisia Gentileschi, Judith Slaying Holofernes, 1613, Galleria degli Uffizi, Florence. Detail.
Judith is a devout Jewish woman, and her faith strengthens her to find a way to overcome the Assyrian invaders. She believes in delivering Israel from its enemies and decides to personally seek out King Holofernes. Judith and her maid Abra approach Holofernes and Judith charms him with her beauty. While they drink wine and eat dinner, Judith offers herself as a lover to Holofernes and as a traitor to the Israelites. Holofernes finds Judith sexually attractive and readily accepts her offers. However, before Holofernes can consummate his lust, he falls asleep drunk with wine. Judith seizes her opportunity and has Abra hold Holofernes while she severs his head from his body! The decapitated body is left in the tent, while the prized head is stolen and taken back to Bethulia. Judith then proudly displays the murdered king’s head on the fortified city walls. The Assyrian army sees its dead king, and flees away in horror and defeat.