New Defender's Study Bible Notes
6:18 Praying always. Persevering prayer, not just for personal deliverance, but also in supplication for others, is the invisible, but powerful, weapon that assures that God Himself, with His angels, is also fighting for us.
6:19 mystery. Once again (see also Ephesians 1:9; 3:3-4,9; 5:32), as he closes the epistle, Paul speaks of that past mystery hidden in God since creation, which he now wants boldly to make fully known.