Alencastre's personal mission included continuing to expand the number of schools and parish churches in the Islands (and to renovate the existing ones) and to build a seminary to form vowed religious locally to the priesthood.

The bishop was also partly responsible for the increase in the variety of religious orders in Hawai‘i, inviting such groups as the Sisters of St. Joseph of Carondelet and the Maryknolls[4] to help spread of Catholicism in the Hawaiian Islands.

Following his death, he was posthumously awarded the honor of "Officer of the Order of the Crown" by King Leopold III of Belgium, while a street in Honolulu bears his surname.

After continuing and completing much of the work begun by Alencastre and his Sacred Hearts predecessors, the mission area of the Hawaiian Islands was elevated to the status of the Diocese of Honolulu by Pope Pius XII a few months following his death.

The history of the Catholic Sacred Hearts mission in the Hawaiian Islands was documented by one of the congregation's priests and later compiled and published in a book called Pioneers of the Faith.