Luke 12:5

Rather than fearing their persecutors the disciples should fear God more. God has the power to affect eternal, not just temporal, destiny. Jesus was not implying that the disciples would end up in hell if they proved unfaithful (cf. John 10:27-28; 2 Timothy 2:11-13). He was warning them about the possibility of losing an eternal reward. He cited God’s punitive power to deter hypocrisy. This is Luke’s only reference to hell (Gr. geenna), but elsewhere it is a place of eternal torment (cf. Matthew 5:22; Matthew 18:8-9; Mark 9:43-48; James 4:12; 1 Enoch 27:2).

"Jesus taught the reality of hell unambiguously." [Note: Liefeld, "Luke," p. 959.]