Although O'Neill supposedly derived Mourning Becomes Electra from the Oresteia, the myth that actually structures the play's action is overwhelming that of Oedipus. Oedipus was the Theban king who unwittingly killed his father and murdered his mother, bringing ruin to the land. Famously Freud elaborated this myth into his Oedipus complex, the structure through which children are conventionally introduced into the social order and normative sexual relations.
At the center of this complex in what Freud defined as its positive form is the child's incestuous desire for the parent of the opposite sex, a desire possibly surmounted in the course of the child's development or else subject to repression. Its development is starkly differentiated for boys and girls. Both begin with a primary love object, the mother. The boy child only moves from the mother upon the threat of castration posed by his rival, the father. In other words, the boy fears that the father would cut his penis off if he continues to cling to the mother who rightfully belongs to her husband. By prohibiting incest and instituting the proper relations of desire within the household, the Father becomes a figure of the law. In surmounting his Oedipal desires, the boy would then abandon his mother as a love object and identify himself with his father.
In contrast, the girl abandons the mother upon realizing both the mother's castration and her own. To her dismay, neither she nor her mother have a penis. She then turns to the father in hopes of bearing a child by him that would substitute for her missing penis; the girl would become a mother in her mother's place. Thus, whereas castration ends the Oedipus complex for the boy, it begins it for the girl.
The Oedipal drama in its many permutations determines the course of the trilogy. Lavinia, for example, yearns to replace Christine as wife to her father and mother to her brother. Christine clings to Orin as that the "flesh and blood," entirely her own, that would make good on her castration. Brant, in turn, is but a substitute for her precious son. Orin yearns to re- establish his incestuous bond with his mother. But the war, where he would finally assume the Mannon name, forces him from their pre-Oedipal embrace in the first place.
Though titled after Electra, the predominant pair of lovers in Mourning is the Mother-Son. Put bluntly, the male Mannons in some way or another take their female love objects as Mother substitutes, and the women pose them as their sons. The Fathers of the play, Ezra and otherwise, figure as the rival who would break this bond of love. As we will see, what is primarily being mourned here is the loss of this love relation, this "lost island" where Mother and Son can be together.
As Travis Bogard notes, O'Neill wrote Mourning to convince modern audiences of the persistence of Fate. Accordingly, throughout the trilogy, the players will remark upon a strange agency driving them into their illicit love affairs, murders, and betrayals. What O'Neill terms fate is the repetition of a mythic structure of desire across the generations, the Oedipal drama.
As Orin will remark to Lavinia in "The Haunted," the Mannons have no choice but to assume the roles of Mother-Son that organize their family history. The players continually become substitutes for these two figures, a substitution made most explicit in Lavinia and Orin's reincarnation as Christine and Ezra. In this particular case, Lavinia traces the classical Oedipal trajectory, in which the daughter, horrified by her castration, yearns to become the mother and bear a child by her father that would redeem her lack. Orin at once figures as this child as well as the husband she would leave to be with her son.
The various substitutions among the players as structured by the Oedipal drama make the players each other's doubles. The double is also the rival, the player who believes himself dispossessed convinced that his double stands in his proper place. Thus, for example, Lavinia considers Christine the wife and mother she should be.
To take another example, Mourning's male players universally vie for the desire of Mother. The Civil War, generally remembered as a war between brothers, comes to symbolize this struggle. The men's rivalries are murderously infantile, operating according to a jealous logic of "either you go or I go." Because in these rivalries the other appears as that which stands in the self's rightful place within the Oedipal triangle, the rivals appear as doubles of each other as well. Orin's nightmare of his murders in the fog allegorizes this struggle, Orin repeatedly killing the same man, himself, and his father. This compulsive series of murders demonstrates the impossibility of the lover ever acceding to his "rightful place" within the Oedipal triangle—Mother will always want another, producing yet another rival.
In the Oedipal myth, what tears the son away from his incestuous embrace with the mother is the imposition of the father's law. Mourning's principal father, Ezra, serves as figure for this paternal law, though more in his symbolic form than in his own person. Ezra's symbolic form includes his name, the portrait in which he wears his judge's robes, and his ventriloquist voice. Indeed, his symbolic form almost usurps his person. Note how Ezra, in fearing that he has become numb to himself, muses that he has become the statue of a great man, a monument in the town square.
Ezra's death makes the importance of his symbolic function even more apparent. With the death of his person, he exercises the law with all the more force, haunting the living in his various symbolic forms. Thus, for example, Christine will cringe before his portrait, Lavinia will invoke his voice and name to command Orin to attention.
The fantasy of the Blessed Island recurs among the major players as the lost Mother-Son dyad disrupted by the Oedipal drama. It, rather than any of their deaths, is the trilogy's principal object of mourning.
Orin offers the most extensive vision of the Blessed Island to Christine in Act II of "The Hunted." A sanctuary from the war, the Island is a warm, peaceful, and secure paradise composed of the mother's body. Thus Orin can imagine himself with Christine without her being there. In terms of the trilogy's sexual drama, the Blessed Island is the realm of the pre-Oedipal, the time of plentitude and wholeness shared by mother and child. However, Orin goes to war to do his duty as a Mannon.
The Blessed Islands are also populated, in the players' imaginations, by natives, which entwine their fantasies of sex with those of race. Generally the native appears through two divergent images: the sexual innocent and the sexually depraved. Thus, for example, Lavinia will recall the islands as the home of timeless children, dancing naked on the beach and loving without sin. This island is the perfect home for a prelapsarian love affair. For Orin, however, the natives display an almost bestial sexual prowess, stripping his sister with their lascivious gazes. The native assumes these proportions when imagined as rivals, the prowess and pleasure they would ostensibly provide the lover becoming objects of envy.
Though Mourning is rife with symbolism, the symbol that dominates the playing space is certainly the Mannon house. The house is built in the style of a Greek temple, with white columned portico covering its gray walls. As Christine complaints in Act I of "Homecoming," the house is the Mannons' "whited sepulcher." It functions not only as crypt to the family's dead but also to its secrets. Its founder, Abe Mannon, designs it as a monument of repression, building it to cover over the disgrace that sets this revenge cycle in motion. What symbolizes this repression in turn is the house's distinguishing feature, the "incongruous white mask" of a portico hiding its ugliness. This mask doubles those of its residents, evoking the "life-like masks" the Mannons wear as their faces.
In Mourning Becomes Electra you write: "Oedipus was the Theban king who unwittingly killed his father and MURDERED his mother." [Emphasis mine].
It should read: "Oedipus...MARRIED his mother!"
(Oedipus' mother Jocasta did commit suicide after learning her lover was her son. Oedipus however did NOT "murder" her.)