§66

Board-games, card games, athletic games, etc. do not have something in common by which they are defined. 'Game' cannot be given a definition in terms of necessary and sufficient conditions - and this should not worry us. What you've got in the case of the concept 'game' is, "a complicated network of similarities overlapping and criss-crossing: similarities in the large and in the small."

Given that this passage follows immediately from the one about the essence of language it seems clear that one point Wittgenstein wants to make is that we cannot find the essence of language and this should not worry us. This is not because the task is a particularly difficult task of discovery but because 'language' cannot be defined in terms of necessary and sufficient conditions.

Another point we can take from this passage is that we should not always think that definitions in terms of necessary conditions can be given. So if we've been struggling to come up with a definition in terms of necessary and sufficient conditions of some term we should not take this as clear evidence that we've failed to define/explain the meaning of the term in question. We should keep in mind that some concepts are 'family resemblance' concepts.