Why did the farmers of the Constitution think that part of the First Amendment was so important?

They knew that if they were really founding a nation based on liberty and equality and fairness, the people had to have rights. Tired of being arrested for libel and being told what to believe, tired of not being able to take a stand, they created the first amendment to give those rights - speech, press, petition, assembly, religion - to posterity. They included those rights because they knew that those rights was central to the framework of the country.