This movement was important because it helped expose more Mexicans to the idea that they could and should take a more active role in pushing for change in their society.
In the years before 1968, Mexicans were mainly expected to be passive and let government be in control. They typically belonged to organizations such as unions, but these were government controlled and did not really do anything to encourage individual Mexicans to participate in society.
In 1968, this started to change. The student movement was very much an unofficial movement from outside the government. It was being critical of the government and it was doing so in the heart of the country, Mexico City. This showed Mexicans that they could play a role in their own society. When the Tlatelolco Massacre happened because of this movement, it helped to discredit the government, eventually leading to a more modern Mexico in which the people have a more important role in society.