I am currently re-reading tGS, and I'm in ch22, The Last That Could Be Done. Rand is having an internal conversation with "Lews Therin" about how he sealed the Bore.

 

It didn't work, Lews Therin whispered. We used saidin, but we touched it to the Dark One. It was the only way! Something has to touch him, something to close the gap, but he was able to taint it. The seal was weak!

Yes, but what do we do differently? Rand thought.

 

So, I thought, what if the three becoming one refers to saidin, saidar, and the True Power all channeled through Callandor? Since something has to "close the gap", and Rand can now apparently tap into the True Power, would it not make sense to use that which is already tainted to close the gap?

This has been suggested multiple times, and IIRC, there is another thread here, or maybe at the non-spoiler discussion, about this line. And not just the powers, but all ideas.