Depending on the referrer, the format of the letter and the means of writing it will differ. Some may want an email letter, while some will prefer a handwritten note. My answer will be based on an email letter.
Dear Mr./Mrs. ......
I really appreciate you taking the time and energy to provide me a recommendation letter which has helped me get through with my university application. I am happy to tell you that I got the seat in the university, part of which is greatly based off your recommendation letter, without which I might not have a chance to be accepted.
So, I would like to say a huge thank you for the help. I will make sure to keep you updated on any development and will always be indebted to your generosity and kind help.
Slave owners thought of slaves as equipment they took care of them but showed no compassion and when the “equipment” didn’t work it was there fault and not the owners