First a caveat, SC‘s slogan has always been “devote the heart”, not “dedicate your heart”. The English translation is inaccurate. When soldiers salute, they’re indicating they devote their own hearts to the Kingdom of Humanity. Usually before heading off into the battlefield, they solute each other to renew the oath.
In chapter 15. Shadis chewed Connie out for doing the salute wrong. So the salute - put your fist on your left chest - is a military rule that soldiers learnt from day one. Do it the wrong way, you’re going to get your ass kicked. It must be a religious thing given the solemn meaning behind it. That is to say, the last person you’d expect to modify the salute, defying the inviolable military rule is … yep, military officers.
So upon hearing “devote the heart”, I think Hange automatically expected a standard salute from Levi, and she will salute back, like the one in 139, then she is ready to go. That didn’t happen. Levi’s fist straightly came at her.
Here is the thing .We as readers might take some time to understand Levi’s gesture, particularly if we didn’t pay much attention to the salute before or only have a vague memory. But for a veteran who remembers the standard salute by heart and who has done it again and again, when they see a fist they see that person’s heart. It should be on his left chest where his heart rests, it’s his heart’s only place, not coming at …
In a word, Levi devoted his heart to Hange, and she understood it.