‘Withal praying for us also that God may open to us a door for the word, to speak the mystery of Christ, for which I am also in bonds, that I may make it manifest (revealed openly, fully and clearly) as I ought to speak.'
Note that Paul says not a word about his own conditions (except for his bonds), nor seeks prayer for help in preparing his defence. He does not want them to pray for these. He wants them to pray for him to be faithful to his responsibilities in Christ, and that the opportunity may be given for the successful presentation of the word of God. He knew that his Father would see to his private needs, and that the Holy Spirit's help was promised for his appearance before the court (Matthew 10:19-20), so he concentrated on what was important.
‘That God may open to us a door for the word.' Compare 1 Corinthians 16:9; 2 Corinthians 2:12; Revelation 3:8. He was in prison and chained to a Roman soldier, yet he prays for the opening of a door for the word (and not that of his prison). He knew what God could do. Little realised he at that time that the door was already opened and that the letters he was writing would become a major part of the greatest book in the world, the New Testament. But the important thing is that his heart was still set on proclaiming the Gospel.
‘To speak the mystery of Christ.' This is the secret now being revealed by the Apostles and their helpers to the world, that is, Christ, Who in them would their hope of glory (Colossians 1:18), establishing those who responded as the new people of God, to the amazement of supernatural beings (Ephesians 3:9-10).
‘For which I am also in bonds.' Many false teacher pointed to their exertions as proof of their genuineness, so Paul points out that he too suffers for Christ (compare 2 Corinthians 6:4-10; 2 Corinthians 11:18-30).
‘That I might make it manifest as I ought to speak.' Paul is aware of the Tempter who would seek to keep him from speaking boldly in his circumstances and the only thing he asks for himself is the courage and wisdom to speak out at every opportunity, so that he can proclaim and make clear the truth to the world.