I don’t know if this has been answered yet, but I think Aang was trying to show Korra that she needs to learn airbending right away. When he was fighting Yakone, he had every element at his disposal and yet he was able to capture Yakone using only air (then earth to hold him in place, and energy bending). Air is about defensive movements and if Korra were to master that, she’d be able to evade Amon and possibly go into the avatar state. What do you think?