The adjective deilos describes a person who is cowardly, timid, or gripped by fear — one who shrinks back when faced with danger or difficulty. In Jesus' rebuke to his disciples during the storm (Mark 4:40), he asks, 'Why are you deilos?' — challenging them about their lack of faith. In Revelation 21:8, the deiloi (cowardly) head the list of those excluded from the New Jerusalem.
The New Testament's treatment of deilos is urgent and searching. Jesus rebukes it as incompatible with faith (Mark 4:40; Matthew 8:26). Revelation 21:8 places the cowardly at the top of a list that includes murderers and the sexually immoral — indicating that spiritual cowardice, the failure to stand firm in faith under pressure, is a mortal danger to the soul. God's answer to deilos is the Holy Spirit (2 Timothy 1:7) and the promise of Christ's presence (Matthew 28:20). Faith is the antidote to cowardice.