In the original Aramaic which Jesus spoke, the word "merciful" means literally "to get under someone's skin." It means to wear his skin, as it were; to see life from his perspective, to stand in his shoes. It means more than sympathy; it means active empathy or merciful understanding.
Let me illustrate. A prominent minister was holding a weekend seminar at Lake Junaluska, North Carolina, several years ago. He kept noticing a man in the front row nodding sleepily. This aggravated the speaker. Preachers don't like for folks to go to sleep on them. We don't have that problem here since we armed the ushers with those 36-foot extendable fishing rods so they can tap any nodding worshipper on the head.
The speaker at Junaluska though to himself: Wonder why the man didn't stay home if he couldn't stay awake? During the lunch break, a woman approached the speaker and said, "Sir, let me apologize for my husband's drowsiness. He is undergoing chemotherapy. The doctors have given him a medication to control the side-effects, but it makes him very sleepy. I tried to persuade him to stay home today, but he said, "I must go as long as I'm able. I never know when I will no longer be able to gather with God's people."
Suddenly that speaker's attitude toward the drowsy man was transformed. Why? The wife had enabled him to get under the skin of her husband and really understand him. That is the quality of mercy.