The Bill of Rights consists of the first ten amendments of the constitution. These amendments help to protect civil liberties (aka freedoms) for citizens and prevents a tyrannical government structure. The interpretation of these amendments (what they actually mean) is constantly changing today. One thing that all of the original ten amendments have in common is the fact that they were purposely implemented based on past experience.
For example, the freedom of religion is a freedom that many people came to this country for when colonization began. This is still a reason people come to America today, as our structure provides for the freedom to practice the religion of your choice.
Along with this, the framers put in other freedoms like the right to assemble. This concept was based on their organization/meetings held prior to declaring independence from Great Britain.
All of these amendments are still needed today to ensure that America remains a government by the people and for the people.