According to the eternal purpose which he purposed in Christ Jesus our Lord: According to the eternal purpose - Κατα προθεσιν των αιωνων· According to the purpose concerning the periods. This seems to refer to the complete round of the Jewish system, and to that of the Gospel. I have often observed, that though the proper grammatical meaning of the word is ever-during or endless duration, yet it is often applied to those systems, periods, governments, etc., which have a complete duration, taking in the whole of them, from their commencement to their termination, leaving nothing of their duration unembraced. So, here, God purposed that the Jewish dispensation should commence at such a time, and terminate at such a time; that the Gospel dispensation should commence when the Jewish ended, and terminate only with life itself; and that the results of both should be endless. This is probably what is meant by the above phrase.
Which he purposed in Christ Jesus - Ἡν εποιησεν· Which he made or constituted in or for Christ Jesus. The manifestation of Christ, and the glory which should follow, were the grand objects which God kept in view in all his dispensations.