A central theme of Othello is perception. Men are judged by other's perception, controlled by their own, and are often mistaken in it all. Iago declares himself that "I am not what I seem."
In these lines, Iago is announcing Desdemona's elopement to her father. But he does not just announce it. He attempts to control Brabantino's perception. He stresses the word now to give urgency to the situation. He refers to Desdemona as a white lamb, an innocent, and suggests in brutal imagery that she has been captured by Othello. He strips Othello of his status as a man by calling him a ram, and calls attention to Othell's age and race at the same time. He twists and controls the situation by controlling Brabantino's perception.