How do you know it's a love letter?

Somewhere along the way, I picked up the idea that the Bible is "God's love letter to His people." While I don't think this isn't true, I am realizing I have allowed that idea to limit my view of the Scripture. It is so many things. It is the epic story. The story of a God and His people. The story of God declaring Who He Is over generations. The story of Him expanding and further expanding His dominion and glory.