By
Le pélèrinage (The pilgrimage) Van Gogh most probably means the large canvas
De bedevaart van Sint-Guido te Anderlecht (The pilgrimage to Saint-Guidon in Anderlecht), c. 1856-1857 (Brussels, Musées Royaux des Beaux-Arts).
Ill. 140 . The Museum acquired this as early as 1870, whereas the two versions of the
Bedevaart naar Diegem (Pilgrimage to Diegem) did not enter public collections until 1904 (the Musée de Beaux-Arts, Doornik) and 1937 (the Koninklijk Museum voor Schone Kunsten in Antwerp). See exhib. cat. Ypres 1995, pp. 110-114, cat. nos. 123, 126, 130.
In his final remark Van Gogh is referring to the characteristic types that are depicted in these works.