"But there is a higher law than the Constitution, which regulates our authority over the domain, and devotes it to the same noble purposes"

This quote by William H. Seward is describing the idea that there is a greater law than the Constitution that governs our authority over the domain. This higher law is committed to honorable functions, such as justice, equality, and liberty. Seward is suggesting that the Constitution is not the only source of authority which there is a higher law that ought to be respected and followed. This higher law is not necessarily written down, but is rather a moral code that needs to be followed. Seward is emphasizing the importance of morality and justice in governing the domain, which the Constitution ought to not be the only source of authority. He is suggesting that the higher law should be respected and followed in order to make sure that the domain is governed in a just and fair way.