Jamieson, Fausset and Brown on Colossians 1:26

26. the mystery--(See on Ep 1:9, 10; Ep 3:5-9). The mystery, once hidden, now revealed, is redemption for the whole Gentile world, as well as for the Jews, "Christ in you (Gentiles) the hope of glory" (Col 1:27).

from ages--"from," according to Alford, refers to time, not "hidden from": from the time of the ages; still what is meant is that the mystery was hidden from the beings living in those "ages." The "ages" are the vast successive periods marked by successive orders of beings and stages of creation. Greek, "Æons," a word used by the Gnostics for angelic beings emanating from God. The Spirit by Paul presciently, in opposition to Gnostic error already beginning (Col 2:18), teaches, that the mystery of redemption was hidden in God's purposes in Christ, alike from the angelic beings (compare Ep 3:10) of the pre-Adamic "ages," and from the subsequent human "generations." Translate as Greek, "the ages ... the generations."

made manifest to his saints--to His apostles and prophets primarily (Ep 3:5), and through them to all His saints.