In 2003, conservation work began at St Louis Church. The conservation of the oil painting from the main altar, which took place in 2003-2005 under the direction of Jozef Steciński, was an extremely difficult undertaking. The dean and parish priest of St Ludwig's Church, Monsignor Jozef Lapkowski (Jazeps Lapkovskis) (1920-2005), who had rendered great service to Kraslaw, had been striving for it for years. The organisational side of the project was handled by the Centre for Polish Cultural Heritage Abroad of the "Polish Community" Association. The work at St Ludwig's Church was carried out in consultation with the Latvian State Inspectorate for the Protection of Cultural Heritage (Valsts kulturas pieminekl u aizsardzibas inspekcija), with the assistance of the Polish Embassy in Riga, as well as the parish priest and parish council and Kraslaw town authorities.

The conservation of the giant canvas Saint Louis setting out on a crusade (unframed the painting measures 695 x 328 cm) was funded by the Senate of the Republic of Poland and the Ministry of Culture and National Heritage. The conservation work begun in 2003, carried out by a team of conservators under Steciński's direction, and preceded by expert reports and chemical and microbiological tests, confirmed the urgent need for specialist intervention, which had previously been indicated by damage to the paint layer, canvas and frame caused by damage from the Second World War, the damp climate and the church's inadequate ventilation.

The conservation of the historic picture frame was carried out by Jozef Stecinski with funds provided by the Latvian State Inspectorate for the Protection of Cultural Heritage. Thanks to funds provided by the Latvian side, art conservator Kristīne Širvinskas restored the wall painting by Castaldi, which had been discovered on the wall enclosing the presbytery. By decision of the church authorities, the oil painting of Saint Louis setting out on a crusade was moved to the south wall of the presbytery. Castaldi's fresco is on display in the main altar. The conservators also looked under the paintings of the side altars. Traces of wall paintings were discovered there too.

Father Łapkowski died shortly before completion of the conservation of the painting "according to a sketch" by Jan Matejko. After his death, the historic church and St Louis parish in Kraslaw were looked after by Father Martins Kluss, whose pastoral duties were taken over by Father Edward Voroneckis (Eduards Voroneckis) in January 2006.

The cooperation with St Ludwig's parish, which was continued by the Ministry of Culture and National Heritage, resulted in the discovery of more Castaldi paintings and the full conservation of the main altar, which was carried out by a Polish-Latvian team of conservators led by Tomasz Dziuravec and on the Latvian side by Dmitrijs Laščetko. Funding for the project was provided by funds from the Programme of the Ministry of Culture and National Heritage.

Through the 12-year-long project, started in 2003 and ceremonially completed in 2015, thanks to the support and involvement of many people and institutions from both countries, it was possible to restore one of the most beautiful and valuable monuments of the common Polish-Latvian cultural heritage. The project was made possible thanks to the support of the Ministry of Culture of the Republic of Poland, the Ministry of Culture of the Republic of Latvia, the Embassy of the Republic of Poland in the Republic of Latvia, the Latvian State Inspectorate for the Protection of Cultural Heritage, the Latvian State Fund for Cultural Support, the "Polish Community" Association, Bishop Jānis Bulis of the Diocese of Rezekneńsko-Aglońska, priests of the St. Louis Church in Krasław, local government authorities, and the close cooperation of Polish and Latvian conservationists.