Andrea has finally achieved satisfaction, having seen his killer and his friend Horatio's murderers receive violent ends. He sums up the violence that has been committed in the play (nine deaths in total, ten if one counts Andrea's death), and then he describes the various paradises awaiting the heroes of the story, who will spend the rest of eternity in Elysian fields. Horatio will rest with the warriors, Isabella with those who grieve, Bel-Imperia with the vestal virgins, symbols of chastity and purity, and Hieronimo with the musician Orpheus. And as for his enemies, they will all be sent to the deepest pits of hell. The Duke of Castile will take Tityus's place in the talons of a giant vulture; Lorenzo will be spun about on the wheel of Ixion for eternity; Balthazar will be hung from Chimaeara's neck, Serberine will take Sisyphus' place rolling a stone up a giant hill only to watch it fall down again, and Pedringano will be dragged through the boiling river of Acheron. Revenge has the final speech of the play, vows to make the after-lives of the villains of the play a never ending tragedy.
The decision on the part of Kyd to literally give Revenge the last word in the play reflects the thematic message of the final scenes of The Spanish Tragedy: revenge does have the last word, crowding out mercy and all other human emotions, seeking its inexorable satisfaction in an orgy of bloodshed and violence. The final scene implies that Hieronimo's action serves as the fulfillment of justice, but the blood, waste, and carnage of the penultimate scene works against this presumption, seeming to deny the possibility of justice in a world where the machinations of class and power determine the course of men's lives.
The theme of judgment also makes an explicit appearance. Andrea effectively sets up a tribunal of his own, sentencing his friends to heaven and his enemies to hell. What changes this appearance of justice from previous appearances is the fact that justice is served. It is not delayed or deferred, as it was for Andrea, Isabella, Hieronimo, and all the other characters throughout the play. Instead, it is simply dispensed, at no cost, by Andrea.
The ending, then, is not tragic at all. Hieronimo is not annihilated in his quest for vengeance and justice: instead, he will enjoy an eternity of peace and happiness. The wicked will pay for their crimes. It is true that the King and Viceroy have had their royal lines wiped out, but for an Elizabethan audience, this would be a cause for celebration, not sadness. In other words, the scene attempts to completely undo the tragic implications of the play's action, by giving all the good characters happy endings and giving the bad ones sad endings, while wiping out the ambiguities that made Hieronimo and Bel-Imperia such engaging characters.