It might be discouraging for Christians to see studies like this from Pew Research that claim that by 2050, Islam will be the most popular religion in the world. Right now, Christianity holds that position, but there are two main features that are causing this trend to change.
First, birthrates are driving this increase. On average, Muslim women have .8 more children than non-Muslim women. Obviously, that would lead to more people being raised Muslim. However, there is another level to this increase in that it is very hard to leave Islam. You can review stories all over the Internet from extraordinarily diverse sources like the National Review and Vice about the stigma that is attached to people who decide to leave the faith.
In fact, in 2013, the Pew Forum on Religion and Public Life reported on the number of Muslims in a variety of countries who first of all support sharia law, and then the percentage of those who supported sharia law and supported the death penalty for apostasy. The numbers are a little bit misleading in the survey in my opinion, so here is a table that outlines the actual percentages of all Muslims in each of these countries who actually support the death penalty for apostasy.
I hope that you can connect the dots here and add up why Islam is on pace to become the most popular religion in the world by 2050. It doesn’t seem to be due to conversion from other religions who are all of a sudden realizing the truth of Islam. Rather, it seems to be retention of people who are most likely to be Muslims. Because Muslim women are having more children on average than women from other religions and there is an incredible stigma associated with deconversion in many Muslim countries around the world, it is no surprise that most of these children who are born Muslim will remain Muslim.
Even though I am sure that not every person who says they support the death penalty for apostasy would want this penalty incurred on their own family members, growing up in an environment where that is the professed worldview would certainly deter children from converting to any other religion when they are older.
It is really no surprise then when we look at these numbers that Islam is going to grow. I would urge you to consider however that right and wrong are not a popularity contest. If you want to find out which religion is actually true, you need to do your homework. Evaluate the claims made in the Bible and the Quran. Consider the implications of each worldview and how they compare with reality. Even if no one believes a true idea, it still remains the truth, so we don’t want to fall into some type of a popularity contest that really does not mean very much in the long run.