The Sacred Heart of Jesus , burning with love for us, is exposed for all to see. The crown of thorns which surround the heart is a reminder of our own ingratitude of that love.
Devotion to the Sacred Heart dates from the eleventh and twelfth centuries, but it was scattered throughout the Church. It was the visions of Saint Margaret Mary Alacoque, a 17th-century French nun, which fostered increased interest in these devotions , along with increased reception of Communion and observance of Holy Hours.
Pope Leo XIII consecrated all humanity to the Sacred Heart in June, 1899.
See also Sacred Heart of Jesus and Immaculate Heart of Mary windows.