These aren’t the easiest days for a united Europe. Both Eastern and Western Europe are suffering from Brexit fever. The destiny of those who want to be out has been decided — just like the destiny of those who want be in. But it is not a time for despair. It is a time for unity, responsibility and vision. A time to understand how we got to this point and how to find our way out together.

Brexit is, above all, a crisis of faith. After 59 years of the European project — the most successful in human history — many Europeans are less appreciative of what it brings (peace, stability, freedom of movement) than of what it takes (solidarity and patience). No price is too high for peace and freedom. This simple truth fades in people's minds as they forget what war and authoritarianism feel like.

Memories are short. This is particularly true in Ukraine, where the same voices that only two years ago were shocked by Moscow’s disgraceful aggression against Ukraine today call for a return to normal relations with Russia, when the Kremlin is still far from delivering on its obligations.

In a crisis of faith, those who have faith are a part of the solution, not the problem. Nowhere in Europe will you see as much faith in the EU as you do in Ukraine. Not because we are not aware of the EU's drawbacks, but because we are all too conscious of the alternatives.

Wherever the European idea is in retreat, it leaves a vacuum that gets filled with something painfully familiar in Europe’s history: national egoism. The European idea does not get replaced with something new — far from it. It is replaced with greed and narrow-mindedness masked as pragmatism. We're not talking about Churchillian pragmatism and vision. Those who demand an exit from the EU aren't visionaries but people who long for more power and less responsibility.

So, where is Ukraine on this scale between in and out, faith and fear, inspiration and blindness? Ukraine is a part of Europe deeply aware of its own sins — and it wants to move forward. Despite war, despite Europe's crisis of faith, no price is too high for Ukrainians to become a better nation. Brexit or not, crisis or not, war or not, we will go the way of EU integration. Which means: more fairness and respect, less corruption and post-Soviet absurdity.

When we say we want in, we are not setting a goal for the EU. We are setting a goal for ourselves. We are reminding the EU that what happened in Ukraine in early 2014 wasn’t all that different from the European revolutions of the late 1980s. It was a moment in history akin to the fall of the Berlin Wall — falling in a different part of Europe, at a different moment of Europe’s history, but worthy of Europe’s attention.

Without a drive for freedom, without political courage or a vision for the future, Europe isn’t an entity, only a space. This is an option Euroskeptics are perfectly fine with. But is it a viable option, if we want a better future?

Ukraine chose the European path, and faced an unprovoked military aggression because of its European choice. We think Europe should stick together more strongly. There is no reason for selfishness or retreat. Europe needs resolute solidarity. Ukraine needs it no less than the Continent does. Territorial integrity and sovereignty must be respected across Europe.

Whatever challenges Europe might face, now or down the line, it needs a sense of vision to stay attractive and on track.

It is the association agreement with the EU that guides Ukrainian efforts to put their home in order, thus making Europe safer and better itself. It shows that Europe's real strength is its ability to inspire change in others. We have to speak about this loudly and with pride to revive the European spirit.

We strongly believe that highlighting EU success stories like trade association agreements or visa liberalization for countries that have faith in Europe is the right reply to those who spread fear, despair and hatred in our common home.

We believe in Europe. We will faithfully stick with Europe. We see Europe for what it is: the only path to a better future and the only remedy for the disease of egoism and division that has cost our Continent millions of lives. As it turns out, even now, after decades of peace and prosperity, Europe isn’t immune. But it can and must fight this disease. Those who believe in a united Europe must pull together. Because today’s choice is not between East and West. It is between those who have faith and those who don't.

It's time for those who have faith in the European project to take the lead.

Petro Poroshenko is president of Ukraine.