I would describe the tone of Jonas's instructions in a few different ways.
I would describe the tone of the instructions as direct. The reason is because several of the instructions are imperative statements. They begin with a verb that directly tells Jonas to do or not to do something.
Go immediately to your dwelling at the conclusion of Training Hours each day.
I grew up in a military household, and the letter reminds me of the way my father interacted with my brother and I. He would tell us to do something, and he expected it to be done. There usually wasn't an explanation. A direct order had been given; it was expected to be obeyed. That didn't make my father unloving. He always had a reason, but he often didn't feel the need to explain it.
I also feel the tone is direct because the letter is so short. There is no flowery language in it. It's a single page document with eight instructions. It is direct and to the point. To Jonas, the instructions are confusing because they don't explain why, but the instructions are very clear in what Jonas is to do.
It's possible to feel that the tone of the instructions is not only direct, but also terse, cold, and impersonal. There is no opening paragraph that says something like, "Hello Jonas! I am so excited that you have been chosen to be the Receiver of Memory. Below are some instructions that I would like you to familiarize yourself with. See you soon!" I understand how a reader could think the instructions feel cold and impersonal. There isn't even a closing section or signature after the eight instructions. It just ends. But as Jonas will come to discover, just because the instructions are direct and slightly impersonal doesn't mean the Giver is an unloving individual.