There are a number of things that interest me about this scene. You can see in the last two gifs how hard it is for Ed to take the gun; it goes against everything he and Al believe in. But he does it because Winry asked him to stay alive, and Riza’s giving him a way of doing so.
Although Riza strongly recommends taking the gun, she still waits for Ed to decide for himself. She gives him a choice. At the same time, Ed must realize that when the Hawk’s Eye is concerned enough to tell him he needs a gun,
that’s a sign some shit is about to go down he definitely needs a gun. I think this scene provides some insight into Riza and Ed’s relationship and the mutual respect they have for each other, and Ed’s final decision shows that he trusts Riza’s judgement even when it conflicts with his own moral compass.