Jamieson, Fausset and Brown on Philippians 3:19

19. destruction--everlasting at Christ's coming. Php 1:28, "perdition"; the opposite word is "Saviour" (Php 3:20).

end--fixed doom.

whose god is their belly--(Ro 16:18); hereafter to be destroyed by God (1Co 6:13). In contrast to our "body" (Php 3:21), which our God, the Lord Jesus, shall "fashion like unto His glorious body." Their belly is now pampered, our body now wasted; then the respective states of both shall be reversed.

glory is in their shame--As "glory" is often used in the Old Testament for God (Psa 106:20), so here it answers to "whose God," in the parallel clause; and "shame" is the Old Testament term contemptuously given to an idol (Jud 6:32, Margin). Ho 4:7 seems to be referred to by Paul (compare Ro 1:32). There seems no allusion to circumcision, as no longer glorious, but a shame to them (Php 3:2). The reference of the immediate context is to sensuality, and carnality in general.

mind earthly things--(Ro 8:5). In contrast to Php 3:20; Col 3:2.