Martin Luther King, Jr. the Baptist; Thomas Merton the Trappist; Dorothy Day, Peter Maurin, and Ammon Hennacy the Catholic Workers, Fritz Eichenberg, the Quaker; Tom Lewis, the Berrigan brothers, the Catonsville Nine; and Jacques Loew, the French Worker-Priest.

What in common did they give to God and humankind? What in particular distinguished their spiritualities or what in particular united their spiritualities?

We cannot say faith in Christ only for we know divinity wasn't the same for all of them, with varying degrees of superstitiousness, for lack of a better term. I'd assert it's their social practice that unites them spiritually. We see the effects of a common, invisible agent (a relationship), a sacrament. And the commonality was that they were the sacrament.