The Tur and the Mechaber write in the first Siman of the entire Shulchan Aruch " טוב לומר" (It's good to say פרשת המן etc.)
If they say that it's a good thing to say it, then we
can rely on them that it's good.
The Mishna Verurah (sk 13) quotes the Bais Yosef
the reason to say it is so to believe that Parnasa comes
with Hashgacha Pratis. The Mishne Verura explains, to believe that increase in Hishtadlus doesn't help to increase Parnasah.
The פרישה quotes the Yerushalmi in Ms.Brochos
(Aruch Hashulchan couldn't find it,) "Whoever says
פרשת המן EVERY DAY* will be guaranteed
not to miss his Mezonos. (Parnasa)
The תשבץ adds "ואני ערב" I am a guarantor.
*not only on Tuesday Parshas Beshalach