(to have) a big part to play

When something has “a big part to play”, it means that it is very important. It wouldn’t be the same without it. Notice that the word “has” goes with this phrase instead of “is”.

See below for additional examples:
 - Alan still has to play a big part to play at Newcastle.
-  Social media has a big part to play  in social government.
-  Supply pressures play big part in driving the market.