I've been considering "shall bind the nine moons to serve him" and what it truly means. This is just one idea that I've come up with.

Saidar and Saidan make up the True Source. They work against each other in order to work in unison and turn the Wheel. Now. We know that in order to control saidan you must fight to get it and the whole thing is a struggle. Saidar is the opposite, you can't fight it. You have to surrender in order to control it.

Now so far Rand has gained the nations through brute force. He has fought and bound them together with blood and fire. What if now, in order to bind the Seanchan (who appear to be as large and powerful or more so than most of the nations on the Mainland combined) he has to basically "surrender" to them. He has to kneel in order to control. Like how Moiraine finally decided to work with Rand. Rand needs to learn when to fight and when to give in. He needs to work and act as the True Source does. He is very strongly ta'veren, after all.

Surrendering is a major theme in WoT. Not sure how many have noticed. Its referred to all the time. From how females channel to "Sheathing the Sword". Even Mat and Perrin. They tried to work against the pattern at one point. They were put into place by the pattern to basically be a defense mechanism as well as Rand was. The three have to work together and work with the pattern instead of against it.