I can't comment on other therapists, but the one in this article is talking about mattering in terms of being engaged with another human being in the moment, that to him it feels that he matters because he is being present with someone. The energy is there, flowing back and forth between people, each separate but also in community. It seems like he's talking about his own human need fulfilled through work. Not all people find that they matter at work, but he does. So I see his comment in that light. I used to feel that I mattered at work. I don't any more. It's not a good feeling.