'Prisoner' in the Bible

praying at the same time for us also, that God may open for us a door of the message, to speak the mystery of Christ, for which also {I am a prisoner},

Aristarchus, my brother-prisoner, sends his love to you, and Mark, a relation of Barnabas (about whom you have been given orders: if he comes to you, be kind to him),

I, Paul, give you this word of love in my handwriting. Keep in memory that I am a prisoner. Grace be with you.