Remember Jesus warned the disciples about having to face persecution, about being brought up before councils, and it would turn to them for a testimony? He said:
Luk 21:12 But before all these, they shall lay their hands on you, and persecute you, delivering you up to the synagogues, and into prisons, being brought before kings and rulers for my name's sake.
Luk 21:13 And it shall turn to you for a testimony.
Luk 21:14 Settle it therefore in your hearts, not to meditate before what ye shall answer:
Luk 21:15 For I will give you a mouth and wisdom, which all your adversaries shall not be able to gainsay nor resist.
Mat 10:19 But when they deliver you up, take no thought how or what ye shall speak: for it shall be given you in that same hour what ye shall speak.
Mat 10:20 For it is not ye that speak, but the Spirit of your Father which speaketh in you.
Luk 12:11 And when they bring you unto the synagogues, and unto magistrates, and powers, take ye no thought how or what thing ye shall answer, or what ye shall say:
Luk 12:12 For the Holy Ghost shall teach you in the same hour what ye ought to say.
Likewise the martyr will be given the faith and power they need in that hour. The Holy Spirit of God will enable them to endure that with the joy of the Lord for they know they will be coming home. As He was with the three Hebrew children in the fire, so He will be with those who are called to give their lives for His sake.
Psa 116:15 Precious in the sight of the LORD is the death of his saints.
That says He's watching over them when they die, their willingness to lose their life is precious to Him. This also can testify to us allowing the cross to work death to self in our lives now. If we die to self now, martyrdom is just one step further. Either one requires the indwelling power and strength of the Holy Spirit in our lives to be accomplished in us. You may not have the faith you think it would take to submit to death for His sake, but if the time comes, He will furnish you with what is needed. Remember, the children only had enough manna for the day. He does not give out enough to store up only what is required for the moment. This keeps us dependent.