I've read one article where Lutheran asked why we "Christians" can't celebrate Easter together.

Here's the truth, you don't want to celebrate Easter at all. Easter will be celebrated if you are ready to come along to celebrate Orthodox Easter. Come to our celebration.

It's about you wanting everyone in Christendom to celebrate Lutheran Easter, not the real Easter which is Orthodox. Even if it's like, Multicultural or Ecumenical Easter, it's not a real Easter.

True Christians should not celebrate "a common Easter with all of Christendom", but should convert to Orthodoxy and celebrate Orthodox Easter.

This same thing applies not only to Easter, but to the "unification" of "churches", the adoption of the true faith.

I don't like the term "unification of churches", because, yes, in everyday language we call these communities "churches", but according to genuine Orthodox theology there is no other church than the Orthodox Church. Instead of "churches", they are heterodox and heretical communities.

In fact, instead of uniting the churches, we should talk about heterodox and heretics abandoning their heterodoxy and heresy and accepting Orthodoxy. Uniting the churches would mean that those unorthodox influences would become part of the church, or we ourselves would be forbidden from following Orthodoxy. A church cannot be orthodox and heterodox at the same time.

The only way to "unite the churches" is to get the heterodox and heretics to renounce their faith and accept the true will of Christ, the Orthodox faith.

But, here comes the reason why I believe that "the churches will not unite", why the heterodox will not renounce their faith, and they do not, per se, "need to do so", in a practical sense. Still, it has it's ultimate cost.

In the crossfire are the preservation of cultural heritage and the true Christian faith.

Heterodox and heretical communities are usually allowed to exist because they maintain the cultural heritage of nations, which are strongly intertwined with heterodox "faith". What would the Italians, the Spanish, the French, the Irish be without Catholicism? They are Catholic cultures. Orthodoxy is Karelian, Russian, Greek, Serbian and so on, there is nothing Finnish about it, Finns are supposed to be Lutherans.

The only people who find it easiest to join the Orthodox Church and embrace the faith are those who are half of the ethnic group where Orthodoxy is part of the culture. Imagine, for example, a Finnish Lutheran who have Karelian/Russian/Greek background, converts to Orthodoxy, he usually does not even have to take a catechumen course because cultural Orthodoxy is already practiced in that family, even though that person was originally baptized as a member of the Lutheran community.

My personal opinion is that those who are ethnically half of the culture where Orthodoxy is practiced should even convert to Orthodoxy to pay for all the injustices of history. Orthodox Christians has experienced a lot of oppression throughout history (and even today in Middle East), which is why its members have baptized their children in heterodox communities.

For example, if someone wants to reconnect with Karelian culture, no self-respecting reconnecting Karelian will remain a member of the Lutheran community, but will leave it and accept Orthodox faith. You are not a member of the Lutheran community for any other reason than the fact that your Karelian relatives were pressured and percecuted by the cultural hegemony of nationalist Finnish Lutherans to give up their own language, culture and faith. So why on earth would you pay church tax to an institution that is the sole reason why Karelian culture and language are currently endangered. Whether you like the fact or not, this is a historical fact, and it is a moral obligation as a descendant of Karelians to leave the Lutheran community. Orthodox Karelians have even been martyred, shot dead by Lutherans, and the Finnish Orthodox Church has its own saint and holy martyr, St. John of Sonkajanranta.

So okay, what is the practical reason why everybody in this world cannot be Orthodox? Everyone who have an ounce of cultural literacy, understands, that heterodox communities and different religions are necessary for cultural presevation of different etnicities. So there's a choice. Either you actually believe in Christ and join Orthodox Church, or abadon your culture completely. And I am not fanatical, I think that having rich culture is more important than having orthodox christian world, because I precisely think that religions are outdated metanarratives and it doesn't really matter what religion you belong in. But in a sense of you claiming to be a real christian and still, you're not orthodox, then you're not a real christian. But does it really matter? Christianity itself is outdated metanarrative, so it doesn't really matter if you don't play along with rules of that game.

Shortly, no, churches cannot unite because y'all are heretics, you're not real christians if you don't convert to orthodoxy, but at the same time, I can see why it's unreasonable to demand people to leave their faith because it means that they leave a lot of their culture behind. And does it matter, when religion is outdated metanarrative replaced by scientific worldview? It matters only if you play with theological rules of christianity and in order to you be the (post)modern human being, you don't even believe in those things so what's the problem? That's why we can't celebrate the Easter together.