Step 1: Understanding the Concept:
This question pertains to the message of Martin Luther King, Jr.'s speech "I Have a Dream". It asks about the spirit in which he urged his followers to continue their struggle for civil rights.
Step 2: Detailed Explanation:
A cornerstone of Martin Luther King, Jr.'s philosophy was non-violence, love for enemies, and an unshakeable faith in the future. In his "I Have a Dream" speech, he explicitly rejects bitterness and hatred. He urges his audience to return to their homes in the South, "knowing that somehow this situation can and will be changed." He concludes his speech with a powerful expression of faith: "With this faith, we will be able to hew out of the mountain of despair a stone of hope." While 'love' is also central to his message, 'faith' specifically captures the hope and belief in a better future that he wanted his followers to maintain.
Step 3: Final Answer:
Martin Luther King, Jr. called on his followers to work with faith that justice would eventually prevail. Therefore, option (D) is the correct answer.