"His father caught sight of him, and was filled with compassion."
The prodigal son, while he was still a long way off - a long way from reconcilliation, a long way off from perfection - the Father caught sight of him, and was moved to compassion. That is the meaning of mercy. The Father runs to meet us - almost at the first thought of any movement towards him.
Although many of us may be a long way off in understanding that, the Father does not fail to embrace and kiss us at the moment of repentance. Again and again, that we might learn the meaning of mercy.