The passage comes not from Jeremiah, but from Baruch (iii. 36–38). It is also quoted as from Jeremiah by Augustine (c. Faustin. xii. c. 43): and in the LXX. version the book of Baruch is placed among the works of Jeremiah, e.g., In both the Vatican and Alexandrine mss. they stand in the following order: (1) Jeremiah, (2) Baruch, (3) Lamentations, (4) the Epistle of Jeremy (Baruch c. vi. in A.V.). The passage which Cassian here quotes is constantly appealed to by both Greek and Latin Fathers, as a prophecy of the Incarnation. See e.g. S. Augustine (l.c.) S. Chrysost. “Ecloga” Hom. xxxiv. Rufinus in. Symb. § 5.