The Greek noun phylake means prison, guard, or watch. From the verb phylasso (to guard), it describes both a place of confinement (prison, jail) and the act of keeping watch. It appears about 47 times in the New Testament. The four night watches — evening, midnight, rooster-crow, and morning — are called phylakai.
Phylake appears in some of the most dramatic passages in Acts, where miraculous prison escapes demonstrate God's sovereign power over human confinement. Peter is imprisoned three times (Acts 4; 5; 12); Paul and Silas are imprisoned at Philippi (Acts 16). In each case, God moves sovereignly — angels, earthquakes, open doors — to release His servants. But phylake is also the context for some of the New Testament's deepest ministry. Paul writes his most intimate and joyful letters from prison — Philippians, Colossians, Ephesians, Philemon. The phylake became a platform. 'Now I want you to know, brothers and sisters, that what has happened to me has actually served to advance the gospel... it has become clear throughout the whole palace guard and to everyone else that I am in chains for Christ' (Philippians 1:12–13). Revelation 2:10 contains the great martyr promise: 'Do not be afraid of what you are about to suffer. I tell you, the devil will put some of you in prison (phylaken) to test you... Be faithful, even to the point of death, and I will give you life as your victor's crown.'