So, it's not, it's just the first change to an already existing document. The first article of your constitution describes the legislatives institutions. I (vaguely) know that, I'm not even American.
It is precisely because it is the first amendment in the bill of rights, that demonstrates how highly the value is held. Any other "change" could have been first, but freedom of speech was chosen. The founders were not going to otherwise ratify the constitution without the bill of rights. I find it a bit pointless to say you are not American and vaguely know something in order to demonstrate that you understand the constitution better despite not being so, if you vaguely don't know that the constitution was not ratified without the bill of rights.
Some states (Delaware, Pennsylvania, New Jersey, Georgia, and Connecticut) ratified the Constitution before the Bill of Rights was formally drafted[1] and initially without requiring the Bill of Rights. The Massachusetts Compromise was an agreement that the Bill of Rights would be packaged with the new Constitution (with the BoR being active at ratification, before the Constitution) and was required before some of the remaining states would ratify the Constitution.
It's worth pointing out that the Bill of Rights was ratified 2.0 years after the first elections for national office and 1.5 years after the constitution was finally ratified. [1]