One of the central tenets in Positive Psychology goes as follows: Other People Matter. It was coined by the late Christopher Peterson as the shortest possible summary of research on human wellbeing. Peterson wanted to make the point that having healthy relationships with family, friends, and coworkers turns out to be the strongest predictor of happiness (and oftentimes: health) in most studies on human wellbeing.
A recent study by Nathaniel Lambert et. al titled To Belong is to Matter: Sense of Belonging Enhances Meaning in Life sheds additional light on this relationship. Here´s a shortened version of the article´s abstract:
We found correlational, longitudinal, and experimental evidence that a sense of belonging predicts how meaningful life is perceived to be. Additionally, we found a strong positive correlation between sense of belonging and meaningfulness. Furthermore, we found that initial levels of sense of belonging predicted perceived meaningfulness of life, obtained 3 weeks later. Furthermore, initial sense of belonging predicted independent evaluations of participants essays on meaning in life.
In short, what they are saying is:
Belonging = Meaning
Or, more precisely: If I matter to other people, my life matters.