This excerpt is from the majority opinion in the U. S Supreme Court case of Marbury vs. Madison (1803). It has been paraphrased. The judicial branch has the authority to decide what the law is and how to interpret the law. When two laws conflict with one another, the court must decide how to apply each law.
If a law opposes the constitution the court must decide if the law or the constitution governs the case.
If the courts understand that the constitution is superior to the laws of congress then the constitution, and not the laws, must govern the case.
The constitution confirms that any law opposed to the constitution has no legal force. It is the duty of the courts to uphold the constitution.

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