There are a variety of synonyms for the phrase "concern oneself," such as "care," "worry," "take an interest," "involve oneself," "occupy oneself," and "pay attention to." These phrases all convey the idea of being invested in or focused on a particular issue or situation. Depending on the context, each phrase may carry slightly different connotations. For instance, "care" might suggest a sense of emotional investment, while "pay attention to" may suggest a more detached curiosity. Overall, however, these phrases all represent different ways of expressing a similar idea: that a person is taking an active role in something, either out of a sense of obligation, responsibility, or interest.