These are the “big ten” reasons that go a long way to explain why Christianity is still the fastest growing religion in the world and why it gains converts from the other religions.
I taught world religions for a number of years, and here are some of the lessons I learned, boiled down.
Christianity has developed traditions and denominations that are interesting to study historically speaking, but they add too much for our purposes here. Let’s reduce Christianity down to the basics that most Christian can agree on.
We could indicate some genuine similarities among the religions (e.g. moral law, which is covered only briefly), but certain other writers do that already–all religions are the same! Not quite.
As I see things, here are the main differences between Christianity and the other world religions. The goal here is not to be frivolously insulting towards them. Rather, let’s simply spell out the differences as coolly and objectively as we can.
These differences are being played out in culture and quality of life, right before our eyes, in the spreading of religions, as we scan the globe.
1. Incarnation: Some world religions teach that God reaches down to people through a book, for example, Islam and Sikhism. Christianity reaches out to people with a book, true, but it goes more deeply and teaches the Incarnation of a living person. In other words, Christ is the ultimate reaching down to humanity. It is true that in later Buddhism a Bodhisattva could achieve Nirvana, but instead chooses to remain here to help people. But the deficiency here is that this man (or woman?) is a human and has always been a human. Or a Buddhist could claim that the Bodhisattva is a divine being. But this doctrine developed hundreds of years after original Buddhism, so the doctrine could be just an invention in faraway Japan. In contrast, Christ is the God-man who came down from heaven, a doctrine taught in the epistles shortly after the Resurrection and in the Gospel of John and implied in the Synoptic Gospels. Finally, polytheism says that the gods pop down into the human realm–usually to start wars or pursue sexual relations and sometimes just to speak to humans. However, these stories cannot be tracked through history. In contrast, Jesus lived for over 33 years with his people in Israel, four decades before the destruction of the Jerusalem temple in A.D. 70. He was crucified under Pontius Pilate, a real person. Then his disciples saw him alive and proclaimed him to be Lord of all. And so there is a qualitative difference between the stories in polytheism and the Main Story in Christianity.
See my post 4. Did Jesus Even Exist?
2. Good works and the Afterlife: All world religions emphasize humankind’s doing enough good works (50.001%?) to secure a place in some sort of Afterlife (call it heaven for shorthand). Islam, Sikhism, and Buddhism are good examples. It’s all work, all the time! In contrast, the fullest explanation of New Testament theology says that a personal God offers salvation to people through imputed or gifted righteousness. He has to do this because humans cannot perform enough good works to be assured of their place in heaven in the presence of the thrice-holy God. After they receive this free gift, their place becomes secure.
3. Full grace: From the second point flows another difference. Only Christianity has a fully developed doctrine of grace. Judaism has something similar, and grace is found in the Tanak (Hebrew Bible or Old Testament), but the emphasis is more heavily on law-keeping. Why else do Jews reverently and joyfully touch the Torah scroll at a synagogue service? Muslims say that grace exists in the words “merciful” and “compassionate” that appear at the top of nearly every chapter in the Quran, but the doctrine is not developed. And Islam, mimicking Judaism, is steeped in law keeping. In contrast, the Apostle Paul clearly teaches in Galatians and Romans that grace and righteousness are free gifts, apart from the law.
See the posts:
4. Moral law: Some world religions teach moral law with no personal deity or barely a deity (of sorts). Confucianism and Taoism are examples here, which are considered religions because they do seem to honor Something above the human, and Taoism may contact spirits through rituals and magic. Other religions that have clearly defined deities proclaim moral law, which is beneficial to humanity, on the whole. Christianity also teaches moral law, but offers a personal, intimate relationship with the merciful Lawgiver. The Islamic deity is far removed from humankind because Islam doesn’t have a full doctrine of the Spirit (see no. 8). To sum up, a person can love moral principles, but it is better when the person realizes that a moral God loves him.
5. Spirits and gods: Some religions worship various spirits and gods. Hinduism and Shintoism are examples. A recent half-hour program on NHK world, a Japanese channel that broadcasts here in the US, showed a tour guide leading people in two Shinto shrines that worship a mountain deity that manifests through snakes, and in a shrine whose followers believe that its spirit communicates through a white fox. Children even dress up in white fox makeup to honor this deity. In contrast, Christianity says that demon spirits exist and can harass and deceive people. Any worshiping of spirits outside of Christ is dangerous. In Christ, no one has to fear evil spirits.
6. Judgment and karma: Some world religions teach karma, for example, Buddhism, Hinduism, and Sikhism. The problem is that karma seems to be impersonal. Who controls it? In Hinduism even the gods are subjected to it. In Christianity, God is sovereign, and no impersonal law or principle rises above him and controls him. He’s the ultimate, personal Lawgiver and Judge of good and bad.
7. Rebirth: Some world religions teach samsara or the birth-death-rebirth of humanity: Buddhism and Hinduism, for example. However, Christ teaches in John 3:1-16 that a human is born once through his mother (no prior life), is born again by the Spirit of the living and loving God, lives his life in Christ, and then dies to encounter a personal, loving and merciful God who judges humankind. Samsara is broken in Christ.
8. Pneumatology or the doctrine of the Spirit: It is more fully developed in Christianity than any other religion. Zoroastrianism, founded in ancient Persia, now modern Iran, comes closest, but this poor religion has been beat down almost out of existence by Islam. And Zoroastrianism teaches that the Good Spirit and the Evil Spirit are equals, fighting it out. Christianity says that the Evil Spirit is Satan with his horde of demons, and they are not equal to God. The Quran mentions the spirit about 20 times, but Muslims have to demote “it” to Gabriel because otherwise the full person of the Spirit wreaks havoc on their strict unitarian monotheism. Judaism has something of a pneumatology because the Tanak (Old Testament) mentions the Spirit, but it has been reduced to an impersonal force in some circles of Judaism; otherwise, a full person co-equal with God also wreaks havoc on a strict unitarian monotheism. And the Spirit in the Tanak came on people only intermittently, not as an abiding presence. In contrast, in Christianity, the full person of the Spirit gave birth to the Church in Acts 2. The Church could not exist, let alone thrive, without him. Someone who claims to be a Christian without the Spirit is just a law keeper, not a born-again believer. The Spirit lives in each believer to guide and comfort him and to assure him of God’s love and a secure place in heaven. Christians attribute the spread of Christianity around the globe even today to the Spirit (not the military).
9. Father God: Perhaps the biggest difference is the absence of a loving Father in other religions. Even Judaism falls a little short here. In the Tanak, “father” is mentioned, but not very often. Hinduism doesn’t offer a loving Father because the multiple gods seem to be in competition with each other, and goddesses exist too. Islam doesn’t offer a Father because Muhammad lived in a polytheistic culture, and the gods had sex and produced children. (He misunderstood the Christian doctrine of Fatherhood and Sonship.) Zoroastrianism, as noted, says there are two co-equal deities, one good, the other bad, who are locked in a struggle. It’s hard to see a loving Father there. In Buddhism, it’s difficult to find a personal deity, let alone a loving Father. In contrast, Jesus Christ is the eternal Son of God (so he is not sexually procreated!), and through him we enter into a personal, intimate relationship with his Father. All of us are now his sons and daughters. It’s a privileged position to be.
10. Monotheism: In some of the points, I have mentioned the Father, Son, and Spirit. Christianity is a monotheistic religion, but it is a very special version: Trinitarian monotheism. God exists in three persons who share the same essence or substance in perfect unity–as One God–and we don’t need to get any deeper than that! As for other religions, Hinduism proclaims polytheism, but it is completely different from Trinitarianism. In polytheism the gods don’t share the same essence, certainly not in the Christian sense of the word. In ancient Greek polytheism the gods fought and competed with each other or at least kept their domains separate. Further, Judaism and Islam have to deny Trinitarian monotheism to keep their strict unitarian monotheism. In reply, Christians ask what God was doing all by himself before he made angels and the heavens and the earth. A unitarian theologian could point out that God is self-sufficient and needs no one. This is true and Christians affirm his self-sufficiency. However, in the Trinity, as Augustine explains, God is love because from eternity past he shares love with the Son through the Spirit, and the Son reciprocates through the Spirit. As a result, the love of a personal God as a fully developed doctrine doesn’t exist in most religions and is downplayed in a few, in favor of religious law (e.g. Islam and Judaism). The three persons of the Trinity did not need to share law keeping or the Ten Commandments. Rather, in Christianity love describes God’s essence and is shared among three divine persons and now us. We Christians experience life in the Spirit through Christ for the glory of the Father in our daily lives.
See my post The Trinity: What Are Some Illustrations?
As noted from the start, this post has striven to explain the differences as coolly and objectively as possible. No insults intended.
It is true that Christianity may share a few features with other religions, and some religions like Islam also deny polytheism, to cite only those examples. But all in all, Christianity is qualitatively different in important doctrines, like the nature of God, the winsomeness of Christ (the God-man), the fullness of the Spirit, and the full grace of God. All religions are not the same in the essentials.
And now let’s not keep those differences only in the abstract arena of doctrine or theology. Instead, let’s ask how these differences have played out in cultures throughout time and across the globe.
Those ten points may explain why Christianity is the largest religion in the world, and why it is still the fastest growing one even today. Just two examples: In Africa in 1900, there were about 10 million Christians. and since the 2000’s there are well over 300 million and still growing. In China the underground church numbers in the tens of millions, maybe hundreds of millions.
Christianity will keep spreading, too, if Christians proclaim the simple, Spirit-filled gospel.
Christianity Is Fastest Growing Religion in World
RELATED
Articles in World Religions Outline series (in alphabetical order):
Dr. Jim's Essential Bible Teaching 
the link to Christianity directs to Buddhism. Good article
LikeLike