8. sometimes--"once." The emphasis is on "were." Ye ought to have no fellowship with sin, which is darkness, for your state as darkness is now PAST. Stronger than "in darkness" (Ro 2:19).
      light--not merely "enlightened"; but light enlightening others (Eph 5:13).
      in--in union with the Lord, who is THE LIGHT.
      children of light--not merely "of the light"; just as "children of disobedience" is used on the opposite side; those whose distinguishing characteristic is light. PLINY, a heathen writing to Trajan, bears unwilling testimony to the extraordinary purity of Christians' lives, contrasted with the people around them.

JFB.