He visited missions in Persia, India, China, Korea, and Japan in 1896–97, and in South America in 1909 and later made similar tours.

He married Emma Doll Bailey in 1893 and, together, they had five children, one of whom, Elliot Speer (1898 – 1934), became headmaster of Northfield Mount Hermon School, where he was murdered in his home on campus, on 14 September 1934.

Although he published two articles in The Fundamentals,[5] some have called him liberal because he sided with the Presbyterian Church (USA) and opposed John Gresham Machen during the anti-liberal/modernist controversies of the 1930s.

Basing his views on his own biblical research, Speer regarded these four principles as one of Jesus' key teachings: Purity, Honesty, Unselfishness and Love.

[12] While the initiator of Moral Rearmament, Dr Frank Buchman, held Robert E. Speer in high regard,[10] he used a version of the four principles which had been reworked by Pr Henry Burt Wright from Yale.