Someone might argue that Christianity is the true religion because it is the largest, and that the Bible is the most read book. Well, this is not much to praise, in Europe Christianity was spread by bloody violence and the sword, by all sorts of persecutions, those who were not willing to convert, the pagans had all their property and livelihood taken away, and they could die of starvation.
For example, this is how Christianity spread in Slovakia, Zakon sudnyj ľudem:
1. Before every law, one must change in God's truth. Therefore, Saint Constantine wrote and said in the first law: Every village in which pagan sacrifices or oaths are performed shall be handed over to the temple of God with all the property belonging to the lords in that village. Those who perform sacrifices and oaths shall be sold with all their property, and the proceeds shall be given to the poor.
(even the Stalinist dictatorship was many times milder. Not only was all the property, home, and livelihood of those unwilling to convert confiscated, but they even had to enter into slavery)
Christianity was a small, insignificant sect with only a few thousand people in the entire Roman Empire, which was larger than all of Europe. And Christianity spread very easily when one single person decided on its spread – Emperor Constantine.
This topic is also discussed in an interesting way in this video https://www.youtube.com/watch?v=azxQ_SKdrKI