Jamieson, Fausset and Brown on Ephesians 6:19

19. for me--a different Greek preposition from that in Ep 6:18; translate, therefore, "on my behalf."

that I may open my mouth boldly--rather, "that there may be given to me 'utterance,' or 'speech' in the opening of my mouth (when I undertake to speak; a formula used in set and solemn speech, Job 3:1; Da 10:16), so as with boldness to make known," &c. Bold plainness of speech was the more needed, as the Gospel is a "mystery" undiscoverable by mere reason, and only known by revelation. Paul looked for utterance to be given him; he did not depend on his natural or acquired power. The shortest road to any heart is by way of heaven; pray to God to open the door and to open your mouth, so as to avail yourself of every opening (Jr 1:7, 8; Eze 3:8, 9, 11; 2Co 4:13).