4 It is mainly to expand the kingdom of Christ that We look to the Rosary for the most effective help. On many occasions We have declared that the object which at the present time engrosses Our most earnest attention, is the reconciliation to the Church of nations which have become separated from her. We recognize, at the same time, that the realization of Our hopes must be sought chiefly in prayer and supplication addressed to almighty God. This conviction We again affirmed not long ago, when We recommended that special prayers be offered for this intention to the Holy Ghost during the solemnities of Pentecost; a recommendation that was adopted everywhere with the greatest good will.
Source: Adiutricem (Vatican.va)