for me - a different Greek preposition from that in Eph 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; Dan 10:16), so as with boldness to make known,” etc. 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 (Jer 1:7, Jer 1:8; Eze 3:8, Eze 3:9, Eze 3:11; 2Co 4:13).