A.T. Robertson Commentary Colossians 2:3

"in whom are all the treasures of wisdom and knowledge hidden." — Colossians 2:3 (ASV)

In whom (εν ω). This locative form can refer to μυστηριου or to Χριστου. It really makes no difference in sense since Christ is the mystery of God.

All the treasures of wisdom and knowledge (παντες ο θησαυρο της σοφιας κα γνωσεως). See on Mt 2:11; 6:19-21 for this old word, our thesaurus, for coffer, storehouse, treasure. Paul confronts these pretentious intellectuals (Gnostics) with the bold claim that Christ sums up all wisdom and knowledge. These treasures are hidden (αποκρυφο, old adjective from αποκρυπτω, to hide away, Mr 4:22) whether the Gnostics have discovered them or not. They are there (in Christ) as every believer knows by fresh and repeated discovery.