The Beis Halevi writes that the commandment to love every Jew is a positive commandment.

This implies that the love of every single individual Jew is a separate mitzvah on its own, and therefore, the more Jews one loves, the more mitzvos one accrues. 

The Alter of Kelm points out how unique the mitzvah of Ahavas Yisrael is, for in just one split second, one can fulfill millions of mitzvos at once!