Contented this has nothing to do with Furlong taking The Pledge - potentially, it's a sign of great things to come (4,2,7)

'potentially it's a sign of great things to come' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.

'contented this has nothing to do with furlong taking the pledge' is the wordplay.
I cannot really see how this works, but
'nothing' could be 'o' (looks like zero - 0) and 'o' is found within the answer.
'furlong' could be 'f' (abbreviation for furlong, a unit of length) and 'f' is located in the answer.
'pledge' could be 'promise' (I've seen this in another clue) and 'promise' is found within the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?