He was the author of the Blackstone Memorial (1891), a petition which called upon the United States to actively return the Holy Land to the Jewish people.

Instead he joined the United States Christian Commission (similar to the modern Red Cross) and was stationed much of the time at General Ulysses S. Grant's headquarters as coordinator of medical services for injured combatants.

Renouncing material pursuits, he proclaimed for the balance of his long life, in his preaching as well as in his writing, the premillennial return and rapture of the Christian Church.

He initially focused on the restoration of the Jews to the Holy Land as a prelude to their conversion to Christianity, out of a pious wish to hasten the return of Jesus Christ; but he increasingly became concerned with the Russian government-instigated pogroms in Eastern Europe and believed that it was necessary to create a Jewish homeland in Palestine.

He presented the Memorial to U.S. President William Henry Harrison in March 1891, calling for the American support of a Jewish state in Palestine, at the time an area controlled by the Ottoman Empire.

His petition presaged and paralleled the later ideas of Theodor Herzl, founder of the modern Zionist movement, whose establishment of a Jewish state was outlined in his pamphlet Der Judenstaat (1896).

He sent to Herzl a personal Bible outlined with the specific biblical prophecies transmitted through the Old Testament referring to the restoration of Jews to the Holy Land.

Supreme Court Justice Louis D. Brandeis rediscovered the Blackstone Memorial in 1916 during the period of his raucous, at times anti-Semitic, Congressional appointment hearings.

Brandeis understood the support that Blackstone would raise for the Memorial would enable President Wilson to accept and endorse American Zionism and the later British Balfour Declaration, which set the course for the establishment of the State of Israel.