St. Luke's gospel is known as the Gospel of Mercy because he focuses on this characteristic in the person of Jesus. He has parables and stories about forgiveness that are not included in the other 3 gospels. He also has details in his passion narrative (the story of Jesus' suffering & death) that are not included in the gospels of Matthew, Mark & John.
For example, only Luke tells us that Jesus mercifully healed the severed ear of the High Priest's servant in the garden of Gethsemane. Only Luke has Jesus say on the cross "Father, forgive them for they do not know what they are doing" as he is being nailed to the cross. Only Luke has Jesus say to the repentant thief: "This day you will be with me in Paradise."
It's ironic that this year we hear the Passion according to Luke for this is the Jubilee Year of Mercy. Listen carefully as Jesus shows his mercy even during his passion.