What is the Gol D. Roger's ability 'To hear the voice of all Things' that Rayleigh is talking about? In Chapter 507, Rayleigh was talking about the power 'To hear the voice of all things' that Gold D. Roger has. It seems to explain how he was able to write in the ancient language on the Sky Island's Poneglyph. What is that phenomenon?
As we have seen Luffy being considered as successor of Pirate King. One of the most important fact that support it is the voice of all things. Though in case of Luffy this ability is somewhat incomparable with Gold D. Roger, it allows Luffy mainly to interact with ancient beings. 
The instances where Luffy was able to used this power was:


Understanding Ryuuji(Green millennial dragon from east blue)
Understanding the sea kings from fishman island
Hearing from Zunisha in Zoe island


Although Roger was able to interact with poneglyph Luffy has not shown this power so far.

From above instances, this power is somewhat like voice of heart and seems to be used by fated ones.

Though  Momonosuke talked with Zunisha it is only limited to it and not more.

So, sit back and wait for history of world to unfold then only we will be able to know what exactly it is. As of now it is highly related to successor of the kingdom of D. (who is fated of course) for controlling the treasures and weapons of the kingdom of D.