Paul's instruction to "pray without ceasing" (1 Thessalonians 5:17) may have raised a few questions among the saints in Thessalonica. Are we not allowed to sleep, to work and provide for our family, to spend time with our children or relax? Do we have to be praying twenty fours hours a day? Obviously, Paul did not intend such a literal interpretation to be placed upon his instruction.
So how do we pray without ceasing? Light is shed on this question by asking another question - how can we love God without ceasing? (Surely no one would deny that we should do this.) We can love God without ceasing and still have lengthy periods of the day when we are not actually thinking about him - we are going about our daily business: working, raising a family, etc. (We can also love our husband or wife without ceasing and still not be conscious of them every moment of the day.) How we live our daily life is a reflection of our love for God. Our work ethic reflects our awareness of always being in the presence of God. For example, we carry out our work as if "working for the Lord". (Colossians 3:23) In other words, we bring God into everything we do. Our response to our employer, our fellow employees, the customers we serve, etc, is carried out according to the will of God. And so we are seen to be loving God without ceasing.
Paul did pray without ceasing yet he wrote over a dozen letters that compose almost half of the New Testament while carrying on extensive evangelism and ministering to the congregations he established. When he was engaging in these activities, he was not in conflict with his instruction to "pray without ceasing". Just as loving God without ceasing is linked to our relationship with him, so too is praying without ceasing. Our relationship with God will manifest itself in a healthy prayer life. It certainly did in Paul's life. He can say, "God whom I serve with my whole heart in preaching the gospel of his son, is witness how constantly I remember you in my prayers at all times." (Romans 1:9) Paul prayed throughout the day as his thoughts went to those in need of prayer. "I thank God," he tells Timothy, "whom I serve, as my forefathers did, with a clear conscience, as night and day I constantly remember you in my prayers." (2 Timothy 1:3) And Daniel was a man who prayed without ceasing, not just because he prayed three times a day, but because we see in him a life that was devoted to God. (Daniel 6:10)
The instruction given to the Thessalonian saints is an instruction to us also; we will indeed "pray without ceasing" when we love God without ceasing.