4. understand my knowledge--"perceive my understanding" [ALFORD], or "intelligence." "When ye read," implies that, deep as are the mysteries of this Epistle, the way for all to understand them is to read it (2Ti 3:15, 16). By perceiving his understanding of the mysteries, they, too, will be enabled to understand.
      the mystery of Christ--The "mystery" is Christ Himself, once hidden, but now revealed (Col 1:27).

JFB.