1 Thessalonians 5:17, “Pray continually.” While “Devote yourselves to prayer” emphasizes prayer as an activity, “Pray continually” reminds us that prayer is also a relationship. Prayer is in one sense an expression of a Christian’s unbroken relationship with the Father.
This verse, then, doesn’t mean that we do nothing but pray, for the Bible expects many other things of us besides prayer, including times of rest when we could not consciously pray. But it does mean that if talking with and thinking of God can’t be in the forefront of your mind, it should always be peeking over and ready to take the place of what you are concentrating on. You might think of praying without ceasing as communicating with God on one line while also taking calls on another. Even while you are talking on the other line, you never lose your awareness of the need to return your attention to the Lord. So praying without ceasing means you never really stop conversing with God; you simply have frequent interruptions.
Spiritual Disciplines for the Christian Life (Colorado Spring, CO; Navpress; 1991) p. 67-68.