Prayer and watchfulness
prayer—a sacred term for prayer in general.
supplication—a common term for a special kind of prayer [HARLESS], an imploring request. “Prayer” for obtaining blessings, “supplication” for averting evils which we fear
6:18. The manner in which a soldier takes up these last two pieces of armor is suggested by two Greek participles: “praying” and “being alert.” When the enemy attacks—and on all occasions—Christians are to pray continually in the Spirit (i.e., in the power and sphere of the Spirit; cf. Jude 20). With all kinds of prayers and requests suggests the thoroughness and intensity of their praying. And like reliable soldiers, they are to be keeping alert, literally, “in all persistence” (en pasē proskarterēsei; the noun is used only here in the NT). Their requests are to be for all the saints because of Satan’s spiritual warfare against Christ and the church. In the Greek “all” occurs four times in this verse; three are translated in the NIV and the fourth is rendered as always (lit., “in all times” or “every time”).
The New Testament frequently exhorts Christians not to cease from prayer (e.g. Luke 18:1; Rom. 12:12; Phil. 4:6; Col. 4:2; 1 Thess. 5:17), and here the particular point is that every incident of life (kairos is the word used—see on 1:10 and 5:16) is to be dealt with in prayer. The apostle is aware that this is no light demand to be made. People very easily take their difficulties to their fellows instead of to God. ‘The power of prayer is gained by systematic discipline’ Westcott wisely says. Constancy in prayer and the natural recourse of the Christian to prayer come only as prayer has become a habit of life, and as a person has learnt to keep alert with all perseverance. Keep alert or ‘watch’ was frequently the exhortation of Jesus himself to his disciples, and most significantly at the time when they needed to find strength by prayer for their hour of trial in Gethsemane.