Inasmuch (katho). “In so far forth as” (“according to which thing”), old conjunction, in N.T. only here and 2Co 8:12; Rom 8:26.
Ye are partakers of (koinōneite). Present active indicative of koinōneō, old verb (from koinōnos, partner), to share in either with genitive (Heb 2:14) or dative as here (pathēmasin).
That ye may rejoice with exceeding joy (hina charēte agalliōmenoi). Purpose clause with hina and second aorist passive subjunctive of chairō, with the present middle participle of agalliaō to exult (1Pe 1:8), “that ye may rejoice exulting.” See 1Pe 1:6-8 for this same idea associated with the second coming of Christ as here.