Final answer:
John Locke's main idea was the importance of individual rights and the government's obligation to protect them, which if failed, the people have the right to alter or abolish it.
Step-by-step explanation:
The main idea expressed by John Locke can be identified as A. The importance of individual rights and government's role in protecting them. Locke's political philosophy centered on the concept of the social contract, where a legitimate government operates with the consent of the governed and ensures the protection of natural rights such as life, liberty, and property.
He posited that if a government fails to protect these rights, the people have the right and duty to overthrow it and establish a government that will secure their safety and wellbeing. These principles heavily influenced the founding documents of the United States, including the Declaration of Independence and the Constitution.