Jamieson, Fausset and Brown on Philippians 2:15

15. blameless and harmless--without either the repute of mischief, or the inclination to do it [Alford].

sons--rather as Greek, "the children of God" (Ro 8:14-16). Imitation of our heavenly Father is the instinctive guide to our duty as His children, more than any external law (Mt 5:44, 45, 48).

without rebuke--"without (giving handle for) reproach." The whole verse tacitly refers by contrast to De 32:5, "Their spot ... not ... of His children ... a perverse and crooked generation" (compare 1Pe 2:12).

ye shine--literally, "appear" [Trench]. "Show yourselves" (compare Mt 5:14-16; Ep 5:8-13).

as lights in the world--The Greek expresses "as luminaries in the world," as the sun and moon, "the lights," or "great lights," in the material world or in the firmament. The Septuagint uses the very same Greek word in the passage, Ge 1:14, 16; compare Note,, see on Re 21:11.