The Success of the Assemblies of God
Not even existing when the Twentieth Century began, the AOG rapidly grew into one of the world's largest religions. I do not agree with all these reasons, but here is why
not necessarily in this order of importance)
1) A strong belief in God's Word. The AOG has done a far better job of keeping out modernism than any other Christian group.
2) Arminianism (the belief that a born-again Christian can lose his salvation). The AOG has done a far better job than other Christians in keeping Calvinism out. (There are Calvinist charismatics, by the way).
3) A declining emphasis on speaking in tongues. Early Pentecostals could perform their own miracle--speaking in tongues. Linguists who recorded this see an over-abundance of the same consonants, no pattern of subjects and verbs, and no pattern in the use of the same words. Claims that priests and rabbis heard charismatics speaking in Latin or Hebrew have been discredited. But it gave life to Christians with dead religions. Today, in my OPINION, the AOG is burdened with the doctrine that speaking in tongues is the evidence of the baptism of the Holy Spirit. The new doctrine that you can be filled with the Spirit without the evidence gives the AOG a chance to bypass the problem.
4) My fundamentalist friends (I am a fundamentalist) are dismayed to learn that the New Testament put FAR greater emphasis on spiritual gifts than it does on reading the Bible. Paul devotes entire chapters to explaining the hows and whys of spiritual gifts, which most non-charismatic Christians ignore. The Holy Spirit gives spiritual gifts to edify the church (building up both numbers and strength) and the AOG uses these gifts.
5) They really do go soul-winning. Brethren, I am going to tell you an ugly spiritual truth: the key to building a successful church is to steal people from other churches. When you see a "great, soul-winning church," you'll find that most of its deacons, elders, teachers, and tithers were saved somewhere else; they came to the growing church because they wanted to do something with their lives. Most American megachurches are in the Bible Belt, where they grew by attracting born-again Christians from other churches. But the AOG actually did win unsaved people to Christ in large numbers. And Pentecostals actually do have mega-churches in Catholic countries. And by teaching poorly-educated peasants how to use their spiritual gifts, the AOG is able to keep them.
6) Purification through splits. Without a central leadership, early charismatics could not be controlled. Unsaved charismatics were free to split off into groups that reject the Gospel, reject the Trinity or reject spiritual growth in favor of showing off. The AOG didn't throw them out--they left eagerly.