Romans 15:18
For I will not dare to speak of any of those things which Christ hath not wrought by me, to make the Gentiles obedient, by word and deed, For I will not dare to speak of any of those things which Christ hath not wrought by me, to make the Gentiles obedient, by word and deed,
Paul would not dare to speak of anything except what Christ had accomplished through him to bring the Gentiles to obedience in word and deed. By word and deed means through both preaching and action, through both his words and his conduct. God worked through his revelations, accompanying his preaching with power, and the visions strengthened the evidence for his message, though he spoke of them sparingly.
His authority and success were not grounds for self-exaltation, but evidence of Christ's work through him. Christian service and its results are Christ's work through the worker, not grounds for selfish pride. Fitness for service and effective missionary work come only when conduct is sanctified, and speech and conduct must be sanctified for effective missionary work, especially brain power and the talent of speech.
The verse sets the duty to guard the door of the lips and to speak nothing unadvisedly. Speech is to be sanctified and cleansed from faultfinding, criticism, contention, and retaliation, and kind, tender, encouraging words are to be spoken instead. A deaf ear is to be turned to criticism of others, and harsh provocation is to be met with silence. One's own wrongs are to be confessed with humbling of self before God while the eye is kept fixed on Jesus, who never finds fault except to lay open perils from which He would deliver.