Being able to manage your emotions in the service of a larger goal will be associated with well-being. Basically, it means "to help". Being able to manage your emotions to help a larger goal will be associated with well-being. Details: "Service" means an action or actions to do good to something or someone. A thing "In service" means that the thing is "inside" or "within" the action of "service". The thing is "inside" that time of service. A "of" B = B has A. Therefore, "A in service of B" means "B has [action of doing good] and A is in the [action of doing good]"

Hey Yuta, how are you? In the sentence you provided, the idiom ''in the service of'' means the same as ''in the name of'' or ''for the sake of'' (something), which refer to a reason a person usually gives for doing something. So, as regards the example ''Being able to manage your emotions in the service of a larger goal will be associated with well-being'', it conveys the idea that ''Being able to manage your emotions for the purpose or motive of a larger goal will be associated with well-being''. Below you shall find other examples with the expression ''in the service of'' used in the same sense: E.g.: ''I dare say he likes to quarrel only in the service of an argument.'' E.g.: ''I heard she decided to quit her job in the service of a better one.'' E.g.: ''My friend moved out of her parents' house in the service of a new life.'' E.g.: ''He claims to have run quite a large number of experiments in the service of science.'' Did you get the idea? Hope that helps!!! Should you have any further questions do not hesitate to contact me. I shall be pleased to help.

Here it means the same as "for". In the service of means to "work for". A worker is in the service of their company. In your sentence, the management of emotions is working for the goal of well being. Mangement of emotions is the worker, and well being is the company.