Opening a door for someone is a metaphor for giving that person the opportunity to do something. AT: "God would provide opportunities" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here "chained" is a metonym for being in prison. AT: "It is for proclaiming the message of Jesus Christ that I am now in prison" (See: [[rc://en/ta/man/translate/figs-metonymy]])
# Pray that I may make it clear
"Pray that I might be able to speak the message of Jesus Christ clearly"