Hannah Whitall Smith published the book The Unselfishness of God And How I Discovered It in 1903. As Wikipedia points out, many editions of the book omit three chapters in which Smith explains how she came to believe God saves all.
Here is a post from Dr. Stephen Jones’s blog that includes an excerpt from one of these “lost” chapters.
This testimony is the partial text of chapter 27 of her book, The Unselfishness of God, in the original publication. It was edited out of later editions when published by Littlebrook Publishing, Inc. in Princeton, N. J., because they did not agree with her discovery that, in the end, God had made provision to save all mankind.
One day I was riding on a tram-car along Market Street, Philadelphia, when I saw two men come in and seat themselves opposite to me. I saw them dimly through my veil, but congratulated myself that it was only dimly, as I was thus spared the wave of anguish that had so often swept over me at the full sight of a strange face.
The conductor came for his fare, and I was obliged to raise my veil in order to count it out. As I raised it, I got a sight of the faces of those two men, and with an overwhelming flood of anguish, I seemed to catch a fresh and clearer revelation of the misery that had been caused to human beings by sin. It was more than I could bear. I clenched my hands and cried out in my soul, “Oh God! How canst Thou bear it? Thou mightest have prevented it, but Thou didst not. Thou mightest even now change it, but Thou dost not. I do not see how Thou canst go on living and endure it.” I upbraided God. And I felt justified in doing so.
Then suddenly God seemed to answer me. An inward voice said, in tones of infinite love and tenderness, “He shall see the travail of His soul and be satisfied.” “Satisfied!” I cried in my heart. “Christ is to be satisfied! He will be able to look at the world’s misery and then at the travail through which He has passed because of it, and will be satisfied with the result! If I were Christ, nothing could satisfy me but that every human being should in the end be saved, and therefore I am sure that nothing less will satisfy Him!”
With this, a veil seemed to be withdrawn from before the plans of the universe, and I saw that it was true, as the Bible says, that “as in Adam all die, even so in Christ should all be made alive.” As was the first, even so was the second. The “all” in one case could not in fairness mean less than the “all” in the other. I saw therefore that the remedy must necessarily be equal to the disease, the salvation must be as universal as the fall.
I saw all this that day on the tram-car on Market Street, Philadelphia — not only thought it, or hoped it, or even believed it, but knew it! It was a Divine fact. And from that moment I have never had one questing thought as to the final destiny of the human race. God is the Creator of every human being; therefore He is the Father of each one and they are all His children; and Christ died for every one, and is declared to be “the propitiation not for our sins only, but also for the sins of the whole world” (1 John 2:2). However great the ignorance, therefore, or however grievous the sin, the promise of salvation is positive and without limitations.
It is true that “by the offense of one, judgment came upon all men unto condemnation,” it is equally true that, “by the righteousness of one, the free gift came upon all men unto justification of life.” To limit the last “all men” is also to limit the first. The salvation is absolutely equal to the fall. There is to be a final “Restitution of all things, when, at the name of Jesus, every knee shall bow, of things in heaven, and things on earth, and things under the earth, and every tongue shall confess that Jesus Christ is Lord to the glory of God the Father.” Every knee, every tongue — words could not be more all-embracing.
The how and the when I could not see; but the one essential fact was all I needed — somewhere, and somehow God was going to make everything right for all the creatures He had created. My heart was at rest about it forever.
I hurried home to get hold of my Bible to see if the magnificent fact I had discovered could possibly have been all this time in the Bible and I had not seen it, and the moment I entered the house, I did not wait to take off my bonnet, but rushed at once to the table where I always kept my Bible and Concordance ready for use, and began my search.
Immediately the whole Book seemed to be illuminated. On every page the truth concerning the “times of restitution of all things,” of which the Apostle Peter says “God hath spoken by the mouth of all His holy prophets since the world began,” shone forth and no room was left for questioning. I turned greedily from page to page of my Bible, fairly laughing aloud for joy at the blaze of light that illuminated it all. It became a new Book. Another skin seemed to have been peeled off every text, and my Bible fairly shone with new meaning. I do not say with a different meaning, for in no sense did the new meaning contradict the old, but a deeper meaning, the true meaning hidden behind the outward form of words. The words did not need to be changed; they only needed to be understood; and now at last I began to understand them.