
A side from various legendary accounts about the founding of the church, there remains one historical fact. In 1623, Count Mathias Thurn had a small church built on this spot. After it was completed, an image of Mary was placed in the church so the faithful could meet in prayer and for liturgical devotions. The Count also had a small monastery built next to the church. The first permanent caretakers of the church and the monastery were the Carmelites who for 134 years enlarged and beautified both buildings. As a consequence of the 1781 decree of Austrian Emperor Joseph II, the Carmelites had to leave Kostanjevica four years later.
The monastery and the church were closed for nine years. In 1811, Kostanjevica was entrusted to the care of the Franciscans who have managed it to this day. After the church was destroyed in World War I the Franciscans had it rebuilt in 1924–1929. The stucco was redone and the church was again resplendent in its former beauty.
The image of Mary with the baby Jesus is situated in the middle of the main altar, surrounded by a frame of golden rays. This fresco of our merciful Mother, known also as Our Lady of Kostanjevica, was made by Leonardo Rigo. The fresco of The Coronation of the Blessed Virgin Mary on the ceiling of the church was painted by Giovanni Moro, a Friulian artist.
The stone memorial tablets in honor of the dead are distinctive of the church of Kostanjevica and indicate the closeness which the nobles of Gorica felt towards this place.