For I will not dare to speak - I should be restrained; I should be afraid to speak, if the thing were not as I have stated. I should be afraid to set up a claim beyond what is strictly in accordance with the truth.
Which Christ hath not wrought by me - I confine myself “strictly” to what I have done. I do not arrogate to myself what Christ has done by others. I do not exaggerate my own success, or claim what others have accomplished.
To make the Gentiles obedient - To bring them to obey God in the gospel.
By word and deed - By preaching, and by all other means; by miracle, by example, etc. The “deeds,” that is, the “lives” of Christian ministers are often as efficacious in bringing people to Christ as their public ministry.