This passage continues the context of the last appearance of seven that we saw, which was Numbers 3.43,

“And all the firstborn males, according to the number of names from a month old and above, of those who were numbered of them, were twenty-two thousand two hundred and seventy-three” (Numbers 3.43).

Then in verse 46, the Lord said,

“And for the redemption of the two hundred and seventy-three of the firstborn of the children of Israel, who are more than the number of the Levites…” (Numbers 3.46).

He then commanded what they were to do.

Since we are in the Book of Numbers, we shall continue to find more of these incidental appearances of “seven.”