Why freedom?
Freedom is part of the meaning of life. Freedom means one can use one's mind.
Why the consent of the governed?
Consent is an expression of free will. Without free will, one is not fully alive. The violator of consent reduces the governed to mechanical cogs in the violator's machine of self-aggrandizement. Consent is not agreement to every policy; it is our agreement to have a government.
Why have law?
Law is the specifics of the agreement we make with each other to obtain our freedom. Just law either constrains everyone such that people do not take away each others' freedom, or it provides equality of opportunity to enhance freedom for a greater portion of the population.
Why have a constitution?
A constitution is the core agreement we all make to secure our freedom. It defines the power of the government to make and enforce law, and it limits that power such that government does not take freedom away.
Why ask government officials to take an oath or affirmation to uphold the Constitution?
That is the agreement they make in exchange for the consent of the governed.
Why impeach?
To fulfill Representatives' and Senators' oaths of office.
To uphold the Constitution.
To enforce the law.
To force the government not to exceed our consent.
To make ourselves free.