Saint Gertrude had a deep empathy for the Church suffering, the Holy Souls in Purgatory. At every Holy Communion, she beseeched Jesus for His mercy to be bestowed on them. During one Holy Communion, she experienced the descent into Purgatory with Our Lord. She heard Him say: “At Holy Communion, I will permit thee to draw forth all to whom the fragrance of thy prayers penetrates.” After Holy Communion, Our Lord customarily delivered more Souls than she had dared to ask for.
One time when Gertrude was praying with great fervour for the Holy souls, she asked Our Lord how many Souls His mercy would release, He answered: “My love urges Me to release the Poor Souls. If a beneficent king leaves his guilty friend in prison for justice’s sake, he awaits with longing for one of his nobles to plead for the prisoner and to offer something for his release. Then the king joyfully sets him free. Similarly, I accept with highest pleasure what is offered to Me for the Poor Souls, for I long inexpressibly to have near Me those for whom I paid so great a price. By the prayers of thy loving soul, I am induced to free a prisoner from Purgatory as often as thou dost move thy tongue to utter a word of prayer!” 
Our Savior taught Gertrude for whom she should most ardently pray for. On the day when the community commemorated in common the death of their parents, Gertrude saw the happy souls ascend the darkness of Purgatory like sparks from a flame. She asked Our Lord if all these were relatives. He answered: “I am thy nearest relative, thy father and thy mother. Therefore, My special friends are thy nearest relatives, and these are among those whom I have liberated.” 
GERTRUDE was asked by someone, that when she offered to God all the gratuitous gifts with which He had favoured her, to request that she might have a share in their merit. “As she prayed thus, she perceived this person standing before the Lord, Who was seated on His throne of glory, and held in His hand a robe magnificently adorned, which He presented to her, but still without clothing her in it. The Saint, being surprised at this, said to Him: ‘When I made a similar offering to Thee, a few days since, Thou didst at once take the Soul of the poor woman for whom I prayed to the joys of Paradise; and why, most loving Lord, dost Thou not now clothe this person with the robe which thou hast shown her, and which she so ardently desires, through the merits of the graces Thou hast bestowed on me, though so unworthy of them?’ Our Lord answered: ‘When anything is offered to Me for the faithful departed, I immediately use it for them, according to My natural inclination to show mercy and pardon, either for the remission of their sins for their consolation, or for the increase of their eternal felicity, according to the condition of those for whom the offering is made.'” 
Prayer to Release 1000 Souls from Purgatory
Our Lord told St. Gertrude the Great that the following prayer would release 1,000 Souls from Purgatory each time it is said. The prayer was later extended to include living sinners as well.
“Eternal Father, I offer Thee the Most Precious Blood of Thy Divine Son, Jesus, in union with the Masses said throughout the world today, for all the holy souls in purgatory, for sinners everywhere, for sinners in the universal Church, those in my own home and within my family. Amen.”
Ecclesiastical approbation: M. Cardinal Pahiarca at Lisbon, Portugal, March 4, 1936
This prayer is also found on the Saint’s page of prayers, which is printable.
29. SAINT GERTRUDE THE GREAT: HERALD OF DIVINE LOVE, TAN BOOKS, p. 44.
30. Ibid., p. 45.
Excerpts Published on the web with permission of Tan Books.
31. THE LIFE AND REVELATIONS OF ST. GERTRUDE, p. 253.