May 24th is the feast day of Mary, Help of Christians. This Marian title has its origin with Our Lady's intercession as Christendom fought against her enemies during the Medieval era, especially in the victory of the Christian naval forces over the Ottoman Turks at the Battle of Lepanto.
In the 19th century Pope Pius VII named May 24th, the date of his triumphal return to Rome after being imprisoned by Napoleon, as the feast of Mary, Help of Christians in thanksgiving to Our Lady for his safe return.
Therefore, historically, this Marian title is closely connected with the Church triumphing over her enemies through the protection and intercession of the Blessed Mother.
Mary under her title Help of Christians was the special devotion of St. John Bosco and the Salesian order he founded. This was based on his Prophetic Vision of the Two Columns in which he saw the Church being saved from the onslaught of her enemies through her devotion to Mary, under her title Help of Christians (Sancta Maria Auxilium Christianorum), and the Holy Eucharist.
The below prayer was composed by St. John Bosco to Mary under this title.
Prayer to Mary, Help of Christians by St. John Bosco
Most Holy Virgin Mary, Help of Christians,
how sweet it is to come to your feet
imploring your perpetual help.
If earthly mothers cease not to remember their children,
how can you, the most loving of all mothers forget me?
Grant then to me, I implore you,
your perpetual help in all my necessities,
in every sorrow, and especially in all my temptations.
I ask for your unceasing help for all who are now suffering.
Help the weak, cure the sick, convert sinners.
Grant through your intercessions many vocations to the religious life.
Obtain for us, O Mary, Help of Christians,
that having invoked you on earth we may love and eternally thank you in heaven.