It was at once deeply impressed upon my mind, that, if Mr. Douglass could be persuaded to consecrate his time and talents to the promotion of the anti-slavery enterprise, a powerful impetus would be given to it, and a stunning blow at the same time inflicted on northern prejudice against a colored complexion.
When Douglass published the Narrative, Garrison wrote its Preface. His praise was effusive:

In labors he has been most abundant; and his success in combating prejudice, in gaining proselytes [converts to the abolitionist cause], in agitating the public mind, has far surpassed the most sanguine expectations that were raised at the commencement of his brilliant career. He has borne himself with gentleness and meekness, yet with true manliness of character. As a public speaker, he excels in pathos, wit, comparison, imitation, strength of reasoning, and fluency of language. There is in him that union of head and heart, which is indispensable to an enlightenment of the heads and a winning of the hearts of others. (Narrative Preface, page vi)
Douglass was a busy man. Although he lived at a time when traveling was difficult, a page from one of his appointment books shows that he frequently spoke in different states. A fierce critic of the 1850 Fugitive Slave Law, Douglass spared no words during a heated exchange soon after it became United States law:

It is something to remember that we had him here when the fugitive slave bill was passed, and that the fullness of his indignation, his contempt of compromising legislation, the highest attainment of his eloquence, was listened to by those who packed the hall where he was to speak. Shall we ever forget one scene in Corinthian hall, - a breathless crowd, for Douglass was hurling out anathema against the bill. “Is there a man here who dares to say he has the right to sell his brother?” A voice clearly responded, “I do.” In an instant every eye saw the speaker - the finger of Douglass pointing him out as he stood, one of the outermost tier against the white background. “Turn your face to the wall then!” in withering tones, that must have made its owner wish he had kept silent.