How do we know that parables illustrate doctrine?

The understanding of parables as illustrations of doctrine is rooted in their purpose as disclosed by Jesus Himself. In Matthew 13, He emphasized that parables are not meant to establish doctrine but to illustrate it. The doctrine concerning salvation, the Kingdom of God, and the gospel are conveyed plainly in Scripture. Parables take this established doctrine and provide illustrations that help convey its meanings. Therefore, while parables enrich our understanding, we should not derive foundational doctrines solely from them.