ISB ~ Philippians 1 v6

began a good work:Paul is confident that his readers’ end will correspond to their beginning, i.e., that the graces of their Baptism will lead them to the glory of eternal life. Though God initiates and completes this whole process (2:13), he also asks us to cooperate with his help by striving for holiness (Heb 12:14) and working toward salvation (Phil 2:12). Paul is not saying that the Philippians can be absolutely assured of their salvation any more than he is (3:12-14; 1 Cor 9:24-27) (CCC 1996, 2008-10).

day of Jesus Christ:The Day of Judgment, when the Lord will come again in glory to reward or punish every thought, word, and deed done in this life. See note on 1 Cor 1:8.