Some of the disciples could anticipate having to confess their belief in Jesus before hostile religious and political bodies, both Jewish and Gentile. They should not become anxious about the wording of their testimonies on those occasions. The situations themselves would provide enough intimidation. Jesus promised the Holy Spirit"s help in formulating the proper defense then. The same Spirit that they might feel pressure to blaspheme against ( Luke 12:10) would help them if they remained faithful to Him (cf. Luke 21:14-15; Matthew 10:19-20). Jesus was not speaking about normal preaching situations but giving oral defense under persecution. Luke recorded many instances of this in Acts (e.g, Acts 4:8; Acts 6:10; Acts 7:55; et al.). Modern persecuted disciples have also testified to the Spirit"s supernatural assistance of them that Jesus promised here. [source][source][source]
The total effect of this teaching was to encourage the disciples to testify to their faith in Jesus boldly when faced with temptation to remain silent or to deny their faith (cf. Romans 10:9-10). All disciples need this encouragement frequently. [source][source][source]
" Luke 12:4-34 is tied together by word links which highlight central themes. In addressing the disciples, Jesus is trying to counter two kinds of fear (note phobeomai in Luke 12:4-5; Luke 12:7; Luke 12:32) or anxiety (merimnao in Luke 12:11; Luke 12:22; Luke 12:25-26). Threatening opposition may cause fear ( Luke 12:4; Luke 12:7) and anxiety ( Luke 12:11). Lack of provision for food and clothing may cause anxiety ( Luke 12:22; Luke 12:25; Luke 12:25) and fear ( Luke 12:32)." [1][source]