Convincing them is not my job, but pointing out the scriptures to those reading along I pray helps a little.
You will quote, you will point out Exodus 20 many times over.
All the readers recognize Exodus 20 as the law and as the letter of the law also.
How can Exodus 20 be anything but the book of the law?
Your church is named after one letter of the law.
You live, eat, and breathe, the letter of the law.
There is no difference between the letter of the law that is spoken or written with a finger.
It's all the same and it's called the letter of the law.