What were the key theological differences between Martin Luther and John Calvin?

Martin Luther and John Calvin had key theological differences in their beliefs about predestination and the sacraments. Luther believed in the concept of justification by faith alone, while Calvin emphasized the idea of predestination, or the belief that God has already chosen who will be saved. Additionally, Luther held a more symbolic view of the sacraments, while Calvin believed in a more spiritual presence of Christ in the Eucharist.