On hearing this, Jesus said, “It is not the healthy who need a doctor but the sick.  But go and learn what this means: ‘I desire mercy, not sacrifice.’  For I have not come to call the righteous, but sinners.”

No need to call the righteous,(those who are saved through the blood of Jesus) they are already” good to go”.  Useless to call the self-righteous, because they THINK they are good to go, and don’t need  a saviour.  But the sinner?  Jesus calls out to the sinner, offering freedom from sin, peace in this world when it seems impossible, and eternal love, beauty and peace after this life is over.