The first Congress added a Bill of Rights to the Constitution to address concerns raised by Anti-Federalists and other opponents of the new Constitution, who feared that the federal government would have too much power and potentially infringe on individual liberties. Here are the key reasons:

1. Protect Individual Liberties: Many Americans were worried that the original Constitution did not explicitly guarantee essential freedoms such as freedom of speech, religion, and the press. The Bill of Rights was added to ensure that fundamental rights were protected from government interference.
2. Address Anti-Federalist Concerns: During the ratification debates, Anti-Federalists argued that without a Bill of Rights, the new government could become tyrannical, just like the British government had been. They feared the federal government could abuse its power and infringe on the rights of individuals and the states. The Bill of Rights was a compromise to address these concerns.
3. Promote Trust in the New Government: The inclusion of the Bill of Rights was a way to gain broader support for the new government. Many states, including Virginia, New York, and Massachusetts, had only agreed to ratify the Constitution on the condition that amendments would be added to protect individual freedoms. The Bill of Rights helped secure the confidence of those who were skeptical of centralized power.
4. Limit Government Power: The Bill of Rights was designed to place specific limits on the powers of the federal government, ensuring that certain rights, such as the right to a fair trial, protection against unreasonable searches and seizures, and the right to bear arms, were protected.