The question is asking about a key belief of Calvinism during the 1500s. To answer this, we need to identify the central tenets of Calvinism as it was understood in that historical period.

Solution By Steps

Step 1: Identify the main principles of Calvinism

Calvinism, a theological system developed by John Calvin, emphasizes the sovereignty of God, the depravity of man, and the doctrine of predestination.

Step 2: Focus on the specific belief during the 1500s

During the 1500s, a key belief of Calvinism was the doctrine of predestination, which asserts that God has predetermined the eternal destiny of each person, including their salvation or damnation, before the creation of the world.

Final Answer

A key belief of Calvinism in the 1500s was the doctrine of predestination, which teaches that God has already decided who will be saved and who will be damned.