Readers are warned to stay alert because the Lord will come as unexpectedly as a thief (see also Revelation 3:3; Matthew 24:43; 25:13; 1 Thessalonians 5:2; 2 Peter 3:10). Being ready for his coming requires preparation. Those who are not prepared will lack proper clothing and will find themselves exposed (see Matthew 22:11–13). This imagery refers to two failing churches:
lifeless Sardis, which is told to “wake up” (Revelation 3:2), and
lukewarm Laodicea, which is advised to get proper clothing (Revelation 3:18).