Brutus No. 1 is an Anti-Federalist document, which argued against the Constitution, warning that a strong national government will threaten individual liberties and state power. It was focused on not allowing the government to have a lot of power, as they had just experienced with Britain. They did not want their freedoms to be taken away again, which is what this document argues about.
A strong central government should not be allowed as the national government could overpower the states. Power, once given, is difficult to take back. It also argues about the threat against state sovereignty as states will lose their independence and federal laws would dominate state laws, which would also make states less significant over time.
The Necessary and Proper Clause gives Congress unlimited implied powers (powers that are not explicitly stated), and it could be used to expand federal authority beyond intended limits.
Judicial power would be too high and it would result in federal courts having too much power. Judges serve life terms, making them accountable, and results in them having power for too long. The judicial branch could interpret laws to increase federal power.
Brutus also argues that a large republic can’t represent a large population. Representatives would be too far separated from the people, and it would be tyrannical.
The overall argument is that the Constitution should not be ratified and that a strong central government risks becoming oppressive. More protections for individual rights are needed.