I go back to read the letter you sent, I understand that some of you do not understand me at all, so I had to explain that you understand everything I do.
I go back to read the mail you sent me, understand that some of you don't understand me at all so I need to explain, you understand everything that I do.
I went back to read the letter that you sent back, I understand that some of you do not understand what I am. and, therefore, I have to explain to you everything that I do understand