This continues the incidental numberings of sevens found in the Bible, when Moses wrote that of the Gershonites, Gershon being a son of Aaron,

“Those who were numbered, according to the number of all the males from a month old and above—of those who were numbered there were seven thousand five hundred” (Numbers 3.22).

That was a huge number, but even as the Lord knows the number of hairs upon our heads, so He knew (or knows) every male that brought the total number to 7,500.