In parliamentry systems you can dissolve parliament, requiring an election. It's usually a way to bypass deadlock. Imagine if, when republicans are fucking around with the debt ceiling and pissing off the country, you could threaten to call a snap election and let them answer to voters then and there.
So if this passes it would basically force a national referendum on netanyahu's leadership.
If gantz is pushing this, probably he thinks he can win. That could mean netanyahu's many financial and political crimes being looked into again. Maybe.
It could mean more of a focus on getting hostages back, but it might not lead to much change in gaza:
Gantz’ centrism is not equivalent to Western centrism: Natenyahu’s Likud party and other Israeli nationalists have “gone so right-wing that the center in Israel has changed,” a Middle East Institute think tank fellow told Al Jazeera. Previously serving as Commander-in-Chief of the Israeli Defense Forces, Gantz has overseen two military offensives in Gaza and labeled several Palestinian NGOs terrorist organizations, indicating it is “unlikely” he would improve the conditions for Palestinians living in Gaza