Unto a dispensation of the fulness of the times (eis oikonomian tou plērōmatos tōn kairōn). See note on Col 1:25 for oikonomian. In Gal 4:4 “the fulness of the time” (to plērōma tou chronou) the time before Christ is treated as a unit, here as a series of epochs (kairōn). Cf. Mar 1:15; Heb 1:1. On plērōma see also Rom 11:26; Eph 3:19; Eph 4:13.
To sum up (anakephalaiōsasthai). Purpose clause (amounting to result) with first aorist middle infinitive of anakephalaioō, late compound verb ana and kephalaioō (from kephalaion, Heb 8:1, and that from kephalē, head), to head up all things in Christ, a literary word. In N.T. only here and Rom 13:9. For the headship of Christ in nature and grace see notes on Col 1:15-20.