Half a shekel. — When shekels came to be coined, they were round pieces of silver, about the circumference of a shilling, but considerably thicker, and worth about 2s. 7 d. Of our money. Their average weight was about 220 grains troy. In Moses’s time coins were unknown, and a half-shekel was a small lump of silver, unstamped, weighing probably about 110 grains. The ransom of a soul was doubtless made thus light in order that the payment might not be felt practically as a burthen by any.
After the shekel of the sanctuary. — Without a standard laid up somewhere, weights and measures will always fluctuate largely. Even with a standard, they will practically vary considerably. The “shekel of the sanctuary” probably designates a standard weight kept carefully by the priests with the vessels of the sanctuary. All offerings were to be estimated by this shekel (Leviticus 27:25).
A shekel is twenty gerahs. — Rather, the shekel, i.e.; the shekel of the sanctuary is of this weight. A “gerah” was, literally, a bean, probably the bean of the carob or locust tree (Ceratonia siliqua), but became the name of a weight, just as our own “grain” did. It must have equalled about eleven grains troy.