Originally used of beginning sacrificial offerings, the term broadened to mean any kind of beginning or commencement. Paul uses it twice to highlight the contrast between beginning and continuing. The Galatians began by the Spirit but foolishly tried to complete by the flesh (Gal 3:3). God who began a good work in the Philippians will complete it until Christ's day (Phil 1:6). The aorist participles emphasize the decisive moment of initiation, setting up the irony or confidence of what follows.