Hikaru no Go has Hikaru always wearing the number 5. 5 is the Arc Number of the series. (Such as Hikaru always wears 5, and 5/5 is an important day in the series.) I just thought this was a normal Arc Number, until I discovered that 5 in Japanese is pronounced "Go". - Steak Addicts Anonymous
the mangaka (Hotta Yumi) has commented on that a bunch of times as well in the tankobon.
On that note I was reading Hikaru no Go the other day and I realized that the words Kubabara (the old honinbou man) was talking about how it takes two to get the hand of god (a rivalry) and how said god is all alone and teachers others go in hopes of having someone they can play evenly with. Well I realised that this had to do with Sai's situation. It seems that by the time Sai disappeared he had actually achieved his said hand of god. He literally became the God of Go in the modern world and he taught the next one to acquire the hand of god (Hikaru). When all was achieved he no longer served a purpose in the story. Most people got really pissed at the ending "Hello, Can you hear me?" It seems like a trololol ending with Sai never reappearing. I still can't decide on whether Hikaru or Sai said that quote but on the basis that it was Sai then the author is trying to communicate that hikaru still has a long way to go to achieve his "Hand of God". This is highlighted in the last chapter with the battle between Hikaru and Akira in tourney. -Aster Tatsu Ryuu 77
It may be because I read a different translation but I never got the impression that it was Sai reappearing; more like a Book End reference to what he first said, but it's also a conclusion to the philosophy that "everyone is aiming for the same thing, everyone is bound by Go, listen to them" - that was why Hikaru heard Sai the first time, Go linked them. It is, in a way, Hikaru saying it this time.
While Hikaru may have said this since it was his turn to pass down the "Hand of God", he may have also been saying it because it was how he met Sai. It may be how he, too, will meet the next person in line, unless he and Akira together will make the new "Hand of God" after Sai (Sai said his part was done, and he left it to Hikaru. This may mean it will take ages in line for the Hand of God to actually be revealed if it's this instant win move he speaks of). It could have also been a line used by Hikaru after his own death and, like Sai, remained in the world to play Go, following the same path as Sai. One of the reasons the ending got so many people on edge about it was because it was way too open, and there's no closure on that last quote. There are plenty of possibilities for the last line. It could very well have been Sai trying to come back into Hikaru's life, but it could have also been Hikaru. That, or it could have been nothing more than a line to end the series the same way it began. The instant move being the "Hand of God", however, is a theory all in its own. There are also various possibilities for that, as well.
I believe "Hand of God" is just a mistranslation and the phrase would better be translated as "divine move". A move in go is sometimes called a 'hand' (in Japanese.)