Ezekiel 44-46 is covenant renewal or reiteration of the law. 45:10-12 is a reiteration of the law of just measures. Verse 12 says:
The shekel shall be twenty gerahs; twenty shekels plus twenty-five shekels plus fifteen shekels shall be your mina.
What is the significance of the summation? Why not simply "one mina must be sixty shekels"?
Rashi points out an interesting fact about the threefold division (bold mine):
Le zent in O. F., the 100 (zuz weight). Menahem, however, connected it to the word מִנְיָן, a number (p. 118). We have here 240 “zuz,” [four zuz to a shekel]. From here we derive that the “maneh” of the Sanctuary was double, and they added a sixth to it in Ezekiel’s time, totaling 240 [zuz] (Men. 77a). When Scripture divided it into three parts and did not write simply, “sixty shekels shall the maneh be for you,” it commanded to make from it a weight one third of it, and a weight equaling a fourth of it, and a weight of the ordinary “maneh” as it was originally.
That is, the new mina within Ezekiel's vision is comprised of one-fourth, one-third, and one-whole of its original value.
Three Christian commentaries ranging from the 16th through the 18th centuries (Matthew Henry; John Gill; Jamieson, Fausset & Brown) inferred that Ezekiel's instruction in 45.12 is evidence of three denominations of currency.
For example, the JFB commentary, which also notes the fourth-third-whole as Rashi did, has the following (bold mine):
The standard weights were lost when the Chaldeans destroyed the temple. The threefold enumeration of shekels (twenty, twenty-five, fifteen) probably refers to coins of different value, representing respectively so many shekels, the three collectively making up a maneh. By weighing these together against the maneh, a test was afforded whether they severally had their proper weight: sixty shekels in all, containing one coin a fourth of the whole (fifteen shekels), another a third (twenty shekels), another a third and a twelfth (twenty-five shekels) [Menochius]. The Septuagint reads, "fifty shekels shall be your maneh."
In other words, the intention of this triple division was to prevent cheating the scales.
