Rimbas river basin happens to be the bridge linking Saribas and Krian so that missionaries traveling overland from Betong district to Saratok district would have to pass that area. Some of Rimbas’ early converts perhaps joined the fold during the evangelism of Buda and his company in the late 1860s. In 1885 when Perham visited Rimbas, he found enthusiatic response from the people he met. A catechist for Rimbas was then trained by Perham and Brok. When Leggatt visited Rimbas in 1888, he baptised some candidates.
In early 1900s, the Christian faith was spreading in the Rimbas through the visits of Howell. In 1906, Catechist Brok was sent to work in the Rimbas, and he stayed there for a few years. In 1919, the Bishop visited Debak and confirmed Sujang, and 12 others. Penghulu Sujang became a leading Christian in Rimbas, and later built a chapel. By 1920 a chapel had been built at Babu. Catechist Indit had been looking after the Spaoh area from the early 1900s.
A school was built in Debak in 1926, but the Mission could not supply a teacher. It was not until 1930, that lay reader Martin Nanang was sent there from Saratok to start a school with 15 boys. It was under Nanang that Debak really took off, and became a mission centre for the Rimbas. Linton and Sparrow visited Debak occasionally to celebrate communion. In 1934 a church was built at Debak and was dedicated to St. Christopher. That year Nanang left to attend the Ordination Test School in Kuching. A new school was built in 1939. During the War, the school at Debak was used for the teaching of Japanese. The school was re-opened in 1945 by Jamau.
In November 1947, Barnabas Jamban moved to Debak after his ordination and stayed there for a few months. A new church was built and dedicated in 1950 at Debak. In 1955 Debak became a separate district from Betong when Jamban moved there again. When Jamban retired a year later, Eric Scott moved to Debak and stayed there until 1958. Scott was replaced by Ambrose Dunggat. By this time, there were chapels at Ulu Bayor (St. John), Ng. Ulai (St. Francis) and Trai (St. Paul).
Later, Debak again became a district of the parish of Betong, and was ministered to by priests from Betong. The re-opening of areas of Ulu Rimbas took place in early 1980s. Debak became a parish again on 1 January, 1978, and Chimbie Bunsi was posted there from Lubok Antu as a resident priest. The new St. Christopher’s Church was consecrated on 21 July 1990.