The church holds the relics of Saint Adelphus since the first half of the 9th century.
In the Middle Ages, these relics had become so popular with pilgrims that the Benedictines built a second church nearby (1190–1225, now the village's Protestant church) specially to serve as a shrine, so as to remain undisturbed in their own sanctuary.
The reliquary of Saint Adelphus was later moved back into Saint-Pierre-et-Saint-Paul in the 19th century, after the dissolution of the abbey following the French Revolution.

Among the many works of art inside the former abbey church, the four early 16th-century tapestries depicting the life and the miracles of Adelphus, on display in the upper of the superposed Romanesque chapels (dedicated to Saint Sebastian), are perhaps the most notable.
A strikingly gory scene depicts a knight being forced by divine wrath to devour his own hand after having tried to break the saint's sarcophagus.
The 12th-century baptismal fonts, the 14th-century statue of the Virgin and Child, the 1478 Entombment of Christ, and the 18th-century carved choir stalls are also especially noteworthy.
All these objects are classified as Monuments historiques.
The church holds the relics of Saint Adelphus since the first half of the 9th century. In the Middle Ages, these relics had become so popular with pilgrims that the Benedictines built a second church nearby (1190–1225, now the village's Protestant church) specially to serve as a shrine, so as to remain undisturbed in their own sanctuary. The reliquary of Saint Adelphus was later moved back into Saint-Pierre-et-Saint-Paul in the 19th century, after the dissolution of the abbey following the French Revolution.
Among the many works of art inside the former abbey church, the four early 16th-century tapestries depicting the life and the miracles of Adelphus, on display in the upper of the superposed Romanesque chapels (dedicated to Saint Sebastian), are perhaps the most notable. A strikingly gory scene depicts a knight being forced by divine wrath to devour his own hand after having tried to break the saint's sarcophagus. The 12th-century baptismal fonts, the 14th-century statue of the Virgin and Child, the 1478 Entombment of Christ, and the 18th-century carved choir stalls are also especially noteworthy. All these objects are classified as Monuments historiques.
Église Saint-Pierre-et-Saint-Paul, Neuwiller-lès-Saverne