Pesukei D’Zimrah-Shekalim-Psalm 148
The reason for the mitzvah to give half a Shekel is offered by Rabbi Shlomo Alkabetz (Manot Levi), cited by the Alshich, as follows: It was intended to teach the Children of Israel the importance of unity, that no one should ever think that he ought to be separate from his fellow man. Rather, he should view himself as being merely half a person, and only after joining all other Jews does he become complete. Therefore, everyone gives half a Shekel.
The commentaries wrote, concerning a Haman’s statement to King Achashveirosh that, “There is a certain people scattered and dispersed among the peoples (Esther 3:8),” that the Jews are a people divided and therefore easily conquered. Therefore through Mordecai, did Esther cry out, “Go, gather together all the Jews (4:16), meaning, in order to repair the devices in this gather them together, in unity.
That is why the Torah commanded that everyone gave half a Shekel each year as “ransom for the soul (Exodus 30:12).” For this sin of divisiveness was not yet corrected, not until Elijah will come, who, “Shall turn the heart of the fathers to the children, and the heart of the children to their fathers (Malachi 3:24).” The theSecond Temple was destroyed in punishment for baseless hatred, until God will send Elijah to repair this sin.
Hence the need to inspire the people on the first day of the month of Adar, before the reading of Esther, by giving half a shekel each, to inspire and arouse themselves to correct this sin, just as Esther sought to repair it when she sensed that the time was appropriate for it. (Toledot Yaakov Yosef, Ki Tisa)
Psalm 148 is associated with the song that the entire, unified creation shall sing upon the arrival of the Messiah. It is an expression of a unified world, a unified people, a unified creation. It is appropriate to apply this lesson of the Half Shekel when singing this song each morning as we prepare for Purim.