At the mass demonstration against the terror attacks in France, Prime Minister Benjamin Netanyahu had a simple message for French Jewry: Israel is your home, you are welcome to join us. Israel’s doors are always open to the Jewish people, as they should be — but what about the Jewish people’s doors?

Aliya may be a nice solution for individuals and even whole communities, but it should no longer be the central aspiration for the future of Israel and the Jewish people. What we really need is more Jews, not just to move them from place to place.

Imagine if all of the Diaspora moved to Israel. Israel’s population would roughly double, to about 16 million, and there would be no Jewish communities outside of Israel. Would that be a good thing?

Doubling Israel’s population is not a bad idea. In any case, the UN already projects that Israel’s population will rise by 2 million to about 10 million people by 2050. With some effort and ingenuity, Israel could double its population while protecting and even enhancing its open spaces, environment, and quality of life.

But that is the subject of another op-ed. The bigger issue is not Israel, but the Jewish people.

If the Jewish population of the world stands still, it is effectively shrinking. Two millennia ago, historians estimate that Jews comprised about 10 percent of the population of the Roman Empire. In 1930, when world population reached 2 billion people, there were about 15 million Jews – about 0.75%. Let’s be generous and say that there are 15 million Jews in the world today. If so, Jewish population has already shrunk to under 0.5 percent, or 1 out of every 200 people.

Let’s say that world population levels out at 9 billion some time in the latter half of this century, and Jewish population stays at 15 million. At that point, Jews will be about .16 percent, or 1 out of every 625 people in the world. This would over 4 times smaller than we were in 1930.

Why should it be this way? Why can there not be more Jews in the world instead of fewer? Why can’t we grow?

The answer, of course, is that we can grow, we just don’t want to. The Jewish people has decided not to grow, and therefore to shrink.

Someone who is not Jewish might have trouble fathoming this. Why would a proud and accomplished people decide to fade away into oblivion? Why would such a people not be scrambling to increase its numbers?

We have many explanations, spoken and unspoken. The first is that we are scrambling to hold on to the people we have by bolstering Jewish identity. Sure, we could be doing much more, such as halving tuition for Jewish day schools and doubling the size of the Birthright and Masa programs, but at least stemming the Jewish outflow has become a priority, perhaps even an obsession.

But we seem not to have considered the obvious, complementary strategy: increasing the inflow. Why just combat assimilation? Why not also open the door a crack to those who want to join the Jewish people?

We could blame the orthodox world for making conversion to Judaism so difficult, but that is a cop out. The problem is deeper than that. The bottom line is that we are more afraid of growing than we are of shrinking.

Deep down, Jews feel that size does not matter. What difference does it make if we are 1 out of 200, 500, or a 1000, the unspoken thinking goes – we will always have an outsized impact and be relevant in the world. This is quite an arrogant attitude, really.

Arrogance, however, is the least of it. It is not about having a relative impact, but an absolute impact. If the Jewish people is not about absolute impact, it has no purpose aside from maintaining a dwindling existence for its own sake.

Either we have something to offer the world or we don’t. If we do, it would be better if Jews became 1 out of 100 people – or 90 million out of a world population of 9 billion in 2070. To do this, we would have to double about 2.5 times in 55 years, which means an annual growth rate of a bit less than 3 percent.

Would that be so difficult? Could we find it in ourselves to welcome three to five new Jews per hundred to fold every year? At this rate, the Jewish people would still be a tiny footnote in global demographic terms. But 90 million Jews means that even with a dramatic increase in Israel’s population to 20 million, that the Jewish diaspora – instead of completely gone as in Netanyahu’s implied everyone-moves-to-Israel scenario — is actually much larger.

A modest net growth rate means that there will more Jews in Israel, France, the US, and elsewhere, all at the same time.

Such growth can only come from two sources: births and conversions. It’s great and healthy that even secular families in Israel tend to be larger than in most wealthy countries. Families with three or four kids are very normal in Israel. But precisely because birthrates are already relatively high in the US and Israel, it is not realistic to build on increasing birth rates as the main part of a growth strategy.

So we are left with conversions. Luckily, in this sphere there is ample room for improvement. Indeed, we don’t need to start knocking on doors looking for converts. On the contrary, a good start would be to stop pushing people away so aggressively!

It is tragic that the very people who claim to care most about Jewish survival — the orthodox rabbinate in Israel, for example – are busy questioning and rejecting the Jewishness of thousands of people who have gone to great lengths to join the Jewish people.

One does not have to go back to the beautiful story of Ruth in the Bible to show that current anti-conversion attitudes are a detour from the wide path of Jewish history. Not only in ancient Israel, but for centuries in exile, Jews would risk their lives to welcome converts. Anti-conversion attitudes are mainly a 19th century circle-the-wagons response by orthodoxy in reaction to Reform Judaism.

The issue is not, however, a legalistic debate between the pro- and anti-conversion strains within Jewish sources. This is a matter that goes not only to the heart of Jewish survival, but Jewish purpose.

We need to decide something fundamental. Is our purpose as a people just to survive, and to become prouder and prouder as we shrink further and further? Or did we survive until this pivotal moment in history to make a dent in the enormous questions and challenges posed by the modern age?

We may think that no matter how few we are in numbers, we can always have a great impact. But there is a big difference between being tiny and growing and being tiny and shrinking. If we are growing with a sense of purpose, more will want to join us, and fewer will want to leave.

The Jewish people has made a tremendous stamp on the course of history, including the modern era. But we have not yet found our full voice for the world that we are plunging into. Judging from the past, we do have something to say. Now is the time to grow, not just to survive, but to find our voice.

Saul Singer is the co-author of Start-Up Nation: The Story of Israel’s Economic Miracle. @saulsinger