"Get in" has the meaning of "arrive". But I think it can have other meanings.
Please see the following sentence:
Please get in the spirit of Valentine's day here in Costa coffee shop.
Here what does "get in" mean?
"Get in" has the meaning of "arrive". But I think it can have other meanings.
Please see the following sentence:
Please get in the spirit of Valentine's day here in Costa coffee shop.
Here what does "get in" mean?
Sometimes get in also used as get into, see the examples here, in your case, it means get into the particular mental state, i.e. the spirit of Valentine's day here in costa coffee shop.
It directs the listener to acquire something they now lack, implying they may still join the group if they do so.