How did Henry IV defend his right to appoint bishops?

Henry IV defended his right to appoint bishops by appealing to long-standing tradition and his role as a divinely appointed leader. For centuries, rulers had exercised the prerogative of "lay investiture," where they installed bishops and abbots with the symbols of their office—the ring and crosier—to ensure these leaders could fulfill their duties as royal vassals and instruments of government.12

When Pope Gregory VII challenged this practice, Henry IV resisted, asserting his authority as the divinely appointed vice-regent of Christ. His defense involved several key actions:2

• Political and Religious Defiance: In 1076, Henry and his supporting bishops renounced their obedience to the pope and demanded his abdication.12
• Military and Administrative Power: When faced with excommunication and internal rebellion, Henry sought to maintain his position by force. He eventually invaded Italy, drove Gregory VII from Rome, and installed his own candidate as antipope Clement III.12
• Appealing to Custom: Supporters of the emperor argued that lay investiture was an "immemorial practice" that had historically been accepted and even enjoined by the papacy, viewing the new papal prohibitions as a violation of established order.2