How pleasing are your tabernacles, Lord God of Hosts.

Turgis, 902

The History of the Memorare
Read about the historical accounts behind this efficacious prayer, which was popularized in the 15th century by Fr. Claude Bernard (not Bernard of Clairvaux, as many believe). Fr. Bernard evidently learned it from his own father:

Fr. Claude Bernard, known as the “Poor Priest”, zealously dedicated himself to the preaching and aiding of prisoners and criminals condemned to death. Trusting his charges to the care and intercession of the Blessed Virgin Mary, Fr. Bernard employed the Memorare extensively in his work of evangelization to great effect. Many a criminal was reconciled to God through his efforts. At one time he had more than 200,000 leaflets printed with the Memorare in various languages so he could distribute the leaflets wherever he felt they would do some good.

Part of the reason Fr. Claude Bernard held the prayer in such high regard was because he himself felt that he had been miraculously cured by its use. In a letter to Queen Anne of Austria, wife of Louis XIII, he wrote that he was deathly ill once. In fear of his life he recited the Memorare and immediately began to get well again. Feeling unworthy of such a miracle, he attributed the cure to some unknown natural cause. 

Sometime later, Brother Fiacre, a discalced Augustinian, came to call upon Fr. Bernard. The good brother begged Fr. Bernard’s pardon for disturbing him, but he desired to know how Fr. Bernard was getting along. Brother Fiacre then went on to say that the Virgin Mary had appeared to him in a vision, told him of Fr. Bernard’s illness, told him how she had cured Fr. Bernard of it, and that he was to assure Fr. Bernard of this fact. Fr. Bernard then goes on to write in his letter that he was ashamed of his ingratitude in attributing the cure to natural causes, and asked for God’s forgiveness in the matter.

The Infallible Teaching of the Church

“If anyone does not properly and truly confess in accord with the holy Fathers, that the holy Mother of God and ever virgin and immaculate Mary in the earliest of the ages conceived of the Holy Spirit without seed, namely, God the Word Himself specifically and truly, who was born of God the Father before all ages, and that she incorruptibly bore [Him],  her virginity remaining indestructible even after His birth, let him be condemned.”  -Pope Saint Martin I, The Lateran Council, Canon 3, 649AD (DS 256)