Use context to determine the meaning of the word in bold organic law

Organic law - this is a law that is enacted on the basis of a direct constitution and in a manner different from the procedure for adopting both the constitution and ordinary laws. As a rule, the constitution provides for the adoption of organic laws on the electoral system, the state of emergency, the status of the highest executive and judicial authorities, etc.

Basic principles and rules

Explanation:

Based on the context of Lincolns letter to a Citizen of Kentucky, I think he was most likely referring to basic rules and principles.