John Gill Commentary Exodus 30:13

"This they shall give, every one that passeth over unto them that are numbered, half a shekel after the shekel of the sanctuary; (the shekel is twenty gerahs;) half a shekel for an offering to Jehovah." — Exodus 30:13 (ASV)

This they shall give, everyone that passes among them
that are numbered
And their number, according to Jarchi, was known by what was paid; for he says the sum was taken not by heads, but everyone gave the half shekel, and by counting them the number was known, as follows:

half a shekel after the shekel of the sanctuary ;
that is, after the standard of a shekel kept in the sanctuary as a rule for all; and so Jarchi paraphrases it,

``according to the weight of a shekel, which I have fixed for thee to weigh, the shekel of the sanctuary.'' It was about fourteen pence: a shekel is twenty gerahs; a gerah being the twentieth part of a shekel, it was not quite three halfpence of our money:

an half shekel [shall be] the offering of the Lord ;
which was to be offered to him for the ransom of souls, whose lives were forfeited by sin; and of the redemption of which this was an acknowledgment; and was typical of the ransom price of souls by Christ, which is not silver or gold, but his precious blood, his life, himself, which is given as an offering and sacrifice to God, in the room and stead of his people.

And which is given to God, against whom sin is committed, the lawgiver, whose law is broken, the Judge, whose justice must be satisfied, and the creditor, to whom the price must be paid.