Ephesians 6:19

And on my behalf, that utterance may be given unto me in opening my mouth to make known with boldness the mystery of the gospel.

As Paul constantly prayed for others, he earnestly desired that others should constantly pray for him. The reason why he felt especially in need of prayer was stated in the next verse. He was an ambassador of the Highest, yet he was chained to a Roman soldier; but Paul was not intimidated by the disparity between his true status and that which might have seemed to be his status. Chained though he was, Paul, in those letters he was dispatching from his Roman cell, was destroying the great pagan empire; and there can be little doubt that Paul fully understood this.

The mystery of the gospel ... This is another reference to the mystery of Christ, the mystery of God, etc., as Paul variously identified it. See under Ephesians 1:9.