Jesus told his disciples that those who confess him before men, he will confess before the angels / messengers of God (Luke 12:8), and he said so in the context of persecution. Jesus was at that very time undergoing persecution by the Pharisees and lawyers (cf. Luke 11:53-54), and the disciples, evidently, seemed to be afraid of what was taking place (Luke 12:7). Authorities can be very intimidating figures, when they want to be, whether or not such intimidation is justified. Jesus faced the unjustified threats and tactics of his enemies, but, although his disciples gathered with him, they seem to have been both surprised with what they were witnessing and somewhat fearful.
There can be no theoretical heroes except in the context of entertainment (Shakespearian plays, Hollywood, TV programs etc.). A person is a hero only if that one has done exceptionally well under difficult circumstances, perhaps risking his own life to save another etc. Similarly, the faithful believer cannot be considered faithful, unless he stands fast under difficult circumstances—choosing Jesus against the crowd, committing himself to Jesus in the face of persecution, remaining faithful to Jesus when doing so hurts his own reputation in the social circles, in which he is accustomed to living etc. Confessing Jesus under difficult circumstances solidifies one’s faith in Christ, and, normally, the believer accounts it joy to do so (cf. Acts 5:40-41).
On the other hand, those who succumb to their fears (cf. Luke 12:7) and deny Jesus before men, Jesus will also deny them before the messengers of God (Luke 12:9).
What Jesus is doing in Luke 12:8-9 is expanding upon the division he created in Luke 11:23, where he drew the proverbial line in the sand. Those who are not for Jesus, in the context of persecution, shall be considered against him. Jesus polarized the moment by saying either confess him or deny him before men when you are afraid (cf. Luke 12:7), be either hot or cold, let your yes be yes and your no be no, and in so doing men will be confessed or denied as disciples of Jesus before the messengers of God.
Confessing Jesus before others, especially in seasons when doing so is considered inappropriate (evil, ignorant, dangerous, unpatriotic etc.), not only strengthens the disciple’s resolve, but it also creates a moment that is not easily forgotten or laid aside, including for those folks who are doing the persecuting. Unbelievers would almost need to recall to mind for further consideration (for good or for bad) why believers would act so deliberately foolish, unwise or unethical (according to the unbeliever’s understanding) and permit themselves to be so ill-treated by their enemies.
Aside from offering the enemy fuel for the evil they do and justifying their cruel methods in their own eyes, denying Jesus before others also destroys one’s own work in Christ. Such an act places the believer in the camp of the unbeliever, because this one has denied his association with Jesus before the messengers of God. I don’t mean to say that torturing a believer into submission is accounted by God as justified ostracism. There are types of persecution that will give any enemy what they desire despite their commitment to the Lord, and God has said in Scripture that such a thing is possible (Isaiah 57:16). However, to deny Jesus in order to save one’s job, or reputation in the community is something different.
While it, too, is persecution, it is also a personal choice to deny Jesus in favor of something in the world that one considers preferable. If one succumbs to the enemy due to constant acts of rebuke and constant acts of anger, that is torture, and God has concluded that the spirit of man is able to stand only so much (Isaiah 57:16). As far as judgment is concerned, God is not disturbed over one’s failure once his freewill is taken away by the enemy (viz. physiological breakdown etc.). He is disturbed over what had been done to his servant, but he wouldn’t blame his servant under such conditions. Rather, the Lord is concerned with what one does, while he exercises his own freewill under difficult circumstances.