He collected the money from the firstborn of the Israelites: 1,365 shekels, according to the sanctuary shekel.
Here is the exchange made of the Levites for the first-born. 1. The first-born were numbered from a month old, Num 3:42, Num 3:43. Those certainly were not reckoned who, though first-born, had become heads of families themselves, but those only that were under age; and the learned bishop Patrick is decidedly of opinion that none were numbered but those only that were born since...
Commenting on Numbers 3:40-51
And Moses gave the money of them that were redeemed,.... That were redeemed this way, and not by Levites, as in Num 3:49, but by money, paying five shekels a head: unto Aaron and his sons; to whom the Levites were given; and this money, as a recompence for the deficiency of the number of them, to answer to the firstborn exchanged for them: according...
Of the firstborn of the children of Israel took he the money; a thousand three hundred and threescore and five [shekels], after the shekel of the sanctuary: (q) Or the two hundred seventy and three which were more than the Levites.