According to Pew Research:
Over the next four decades, Christians will remain the largest religious group, but Islam will grow faster than any other major religion, mostly because Muslims are younger and have more children than any other religious group globally. By 2050, the number of Muslims will nearly equal the number of Christians.
The growth of Christianity is keeping pace with world population growth. All other faiths, except Islam, have plateaued or are declining in their percentage share of the world’s growing population. Even the percentage of religiously unaffiliated is declining.
The world is becoming more religious due mainly to the growth in Islam and Christianity. I don’t think anyone predicted this trend.
A generation ago the assumption was the ultimate triumph of secularism.