"Vengeance is mine; I will repay, sayeth the lord" (Romans.xii.19). This Bible verse is quoted by Hieronimo in Act III, scene xiii, and it can be said to epitomize the official Elizabethan attitude toward revenge: that it is something that should be left to God. But this position is silent on the relationship between revenge and justice, which are are identified with each other throughout the play—Hieronimo makes the connection explicitly several times, and revenge is officially sanctioned by Proserpine (Persephone), the Queen of the Underworld, in the play's opening scene. Revenge should be performed by God (or the State, which derived its power from God), but it still needs to be performed. This is the presupposition that underlies Hieronimo's doubts whether the Heavens (and God) are in fact just, which are doubts he expresses after the murder of his son and the apparent escape of his murderers. This link between revenge and justice also explains why, in III.xii, and IV.i, Hieronimo decides to revenge Horatio's death himself and why he interprets Bel-Imperia's offer of help as a sign that Heaven favors his decision. Hieronimo may here consider himself the agent of the divine vengeance that a just God must bring against his son's murderers, the man chosen by God to revenge Horatio's death. His act would thus be a service to God and not an usurpation of God's role.
There is, unquestionably, doubt in the audience's mind as to whether Hieronimo is right, and a similar ambiguity is felt toward other cases of revenge in the play as well—Andrea's and Bel-Imperia's, for example. Exactly what deaths should be revenged and who should do the revenging were topical questions for Elizabethans, who were living in a time when the Elizabethan state was bringing a centuries-old tradition of private revenge in England under control. It was also a state whose preachers advised leaving revenge to God, while at the same time describing the horrible revenge God would take on sinners. But the problems posed to us by revenge—and the intense desire for it when we or a loved one is injured by another, especially when the law fails to provide us with redress—is something that can be felt by modern audiences as well.
Not only is revenge a form of justice in the play, it is, ironically enough, an expression of love. Bel-Imperia's love for Andrea leads her to desire revenge against Balthazar; Balthazar revenges himself against Horatio because he loves Bel-Imperia. Bel-Imperia and Hieronimo make the most explicit connection between the two, interpreting the failure to revenge one's loved one as a lack of love. The presupposition that underlies all these actions and words is that love for a murder victim finds its fullest expression in vengeance. In effect, vengeance is an assertion that the loved one is not forgotten. Thus, Andrea's desire for vengeance is understandable as a desire not to be forgotten by those still living, and love and revenge are intertwined in the symbol of the bloody handkerchief, which starts out as a simple memento but ends by becoming, for Hieronimo, a symbol of both the memory of his son and the need to revenge his son's death.
The wheel of fortune was a potent image in Elizabethan iconography. It signified, in the Elizabethan consciousness, the vagaries and constant revolutions of Fortune, from low to high and everywhere in between. Lorenzo makes an allusion to it when he notes that the social-climbing Horatio is, hanged from the trees, "higher" than he ever was in life, and the Viceroy makes explicit reference to it in mourning the loss of his son in Act I (though his mourning is ironic, because it is premature). From Andrea onward, the characters we meet all experience drastic reversals of fortune—the loss of a son, the loss of life, the loss of a lover. This vicarious experience of the precariousness of human happiness—the way, in an instant, it can be changed to misery—is one of the unique pleasures that tragedy affords us: we are allowed to experience this loss without actually experiencing the tragic loss ourselves.
Kyd uses dramatic irony throughout the play to drive a wedge between the world as his main characters see it and the world as it actually is. Balthazar and Bel-Imperia see their evening rendezvous in the orchard as a safe space in which to express their love, because Bel-Imperia thinks that Pedringano is a trustworthy servant. In fact, Pedringano is deceitful, and, because of his treachery, the orchard turns into a place of death.
Furthermore, Lorenzo enthusiastically agrees to play his part in Hieronimo's tragedy, not knowing that Hieronimo intends not only his character to die, but for him to die as well. But, perhaps the most concrete and dramatic example of this wedge is Pedringano's belief that a pardon is contained inside the box Lorenzo has sent him. The box then comes to symbolize, in the view of many critics, a more fundamental and general limitation on human knowledge. In other words, the characters' inability to get past appearances is typical of all human beings' inability to penetrate appearances.