Might help to look at idea of Strict Constructionism, as a particular legal philosophy of judicial interpretation that limits and restricts variety of interpretation regarding laws.
In opposition to it, we have Liberal Constructionism, which leaves room for different meanings and interpretations regarding each part of the constitution.
Now let's look at how the restrictions of the Constitution and congressional power interact:
Our Constitution defines and limits what powers the government may impart. It basically represents what we have agreed to let the government do for us (or to us). To change such a thing should require broad input and consent from the stakeholders (us). Imagine what life would be like if Congress, the President, or the Supreme Court could just strike some text from the Constitution when it happened to be politically convenient. Too many protests about a war? Too many whistle blowers? They just pass a new amendment that repeals the first amendment and all trouble is gone for the government, but at what cost?
The difficult process and restrictions to congressional power are there because we need to consider just how willing everyone is to agree to the proposed changes.
Hope this helps!