The correct answer to this open question is the following.
The cause is Bryan comparing to “the cause of liberty” and “the cause of humanity” is the free silver policy.
We are talking about an important speech delivered by Nebraska's legislator William Jennings Bryan on July 9, 1896. The speech was known as the "Cross of Gold Speech," and was the speech that impacted the most during the Democratic Party Convention in Chicago, Illinois.
Bryan compared “the cause of liberty” and “the cause of humanity,” when he said in his speech, the following:<em> "The humblest citizen in all the land, when clad in the armor of a righteous cause, is stronger than all the hosts of error. I come to speak to you in defense of a cause as holy as the cause of liberty—the cause of humanity."</em>
In that convention, Bryan supported the use of silver, not only gold, as the standard for the United State. He considered that the addition of silver would impulse the US economy.
