Othello in answering the concerns of the duke says:
That I have ta'en away this old man's daughter,
It is most true; true, I have married her:
The very head and front of my offending
Hath this extent, no more. Rude am I in my speech,
And little bless'd with the soft phrase of peace:
For since these arms of mine had seven years' pith,
Till now some nine moons wasted, they have used
Their dearest action in the tented field,
And little of this great world can I speak,
More than pertains to feats of broil and battle,
Othello's admission that his nature is warlike and not much given to the phrases and speech of peace is a vital part of the foreshadowing of the difficulty he will face when the possibility of war is removed following the Turkish fleet's disaster.
At this point his confidence is very high, given that he goes off to war, something he knows well and gives him purpose. But once that purpose is lost, his mind is easily beset by the jealousy that Iago weaves into it so skillfully.