1. The Star of David is sometimes used as a religious-Judaist symbol. However, it's also used to represent both secular and religious Israeli nationalism (Zionism).
2. Even if the Star of David was purely religious-Judaist, it doesn't make the State of Israel religious. The national motto of the US is religious ("In God We Trust"); does it make the US religious?
1) Whether it sometimes also represents "Zionism" or a nation for the Jewish ethnicity does not change the fact that it is also often used as a religious symbol. And no matter if it were perceived as a symbol of the ethnic Jewish people or of Judaism it still excludes every other group symbolically by existing as a national symbol. This doesn't mean that Israel is an authoritarian theocracy, but it does give preferential status to a specific group in its constitution and in practice when it has had full control over Palestine before. This represents an area that would need change if the next Israeli administration wants to become serious about long term reforms that include the Palestinians (assuming there is no hope for a two state solution, which is a big assumption).
2) The US has the motto "in god we trust" which causes an incredible amounts of friction between hardline religious conservatives and most center right to left wing policy proposals, despite the "in god we trust" slogan not even representing any particular religion. This friction does interfere in and influence politics. In Israel the friction is much worse because a much more significant portion of their right wing is demanding an ethno state and the continued suppression/ forcible removal of the Palestinians.
I am arguing that to become a fully secular state Israel would need to change its flag and the constitution to give equal status to the Palestinian Arabs, many of whom alive today were displaced within the past century by European immigrants to the region.
It would be like if the USA had a white cross on a red background as its flag to represent the broader "white European Christian community" and had provisions that were still in effect in its constitution that directly mention evangelical Protestants from around the world as having prioritized citizenship rights and stating that the USA is specifically meant to be a "white evangelical homeland under the flag of the blazing cross".
Trust me, things can get bad sometimes in the USA, but nowhere in our constitution (even in the original believe it or not) does it say that the USA is a white evangelical Christian homeland and that white people or evangelical Christians get prioritized citizenship over everyone else. We also do not have a flag with a giant white cross on it. If it were there would be justified mass protests and social upheaval to get both changed.
I don't say this to be critical of the Israeli people or the state itself, but the political leaders of Israel and some of its conservative populous need to recognize this and consider making a change to live side by side with the Palestinians if they can not accept a 2-state solution and insist on control of Palestine.
This is just my opinion though. I'm sure many Israelis are already concerned about what is going to happen next when Israel takes full control of Gaza. Im sure nothing I've said probably hasn't already been said within Israel.