I read it in wiki.
The best I can make out is that these are the reasons:
"patterned after the capstone of the Great Pyramid of Egypt, symbolic of the Christ"
and that Russell made (superstitious) predictions based on measurements in the pyramid.
"Russell had first published that the date 1874 was derived from a measurement of 3416 pyramid inches [105] which measurement was revised in the 1910 edition to 3,457 inches (87.8 m) to point to 1915."
Now, even some of the christian religions say there is some great mystery to reveal Plan of Ages and pyramid has something to do with that.
And I have seen this scripture used to say it is refering to the great pyramid.
Isaiah 19:19:In that day there will be an altar to the LORD in the heart of Egypt, and a monument to the LORD at its border. 20:It will be a sign and witness to the LORD Almighty in the land of Egypt.
So, if the great pyramid is really some sort of "witness to god" or holds some sort of key to the Divine Plan...what is it? What makes it so?
How is the great pyramid a witness to god? (Or does russell's idea of it make sense to you?)