So, what did he say was "the greatest thing in the world?"

Scotsman Henry Drummond insisted he knew the answer based on what he considered the highest authority. He spoke of the "greatest thing" often. In fact he was invited all over the world to talk about it. The title of his little talk was simply The Greatest Thing in the World. You can read it in ten or fifteen minutes. It has never been out of print in the 120 years since first published and maintains its status as a classic of spiritual inspiration.

What did Henry say was the greatest thing?

You'll have to read the book to find out...