Which concept did John Calvin strongly reject?

John Calvin strongly rejected the idea of alliances with civil government, which reflects his belief in the separation of church and state. He advocated for the sovereignty of God over all aspects of life, including governance, and was critical of any entanglement between religious authority and political power that compromised the church's spiritual integrity. In Calvin's view, the church should guide moral and ethical aspects of society without being co-opted by civil authorities.

The other concepts mentioned are important to understanding Calvin's theology. Calvin maintained that faith alone is central to salvation, emphasizing that human effort is insufficient for redemption, which aligns closely with the Protestant Reformation's teachings. He believed that God's grace, while predestined for the elect, is pivotal in the salvation process, though he would argue that it isn't universally available to everyone as common grace—meaning the grace available to everyone received individually in personal faith—which could create a misunderstanding. However, his rejection of alliances with civil governments was clear and fundamental to his theological stance, underlining a commitment to a distinct understanding of the roles of church and state.