"The Pharisee, standing by himself, was praying thus, 'God, I thank you that I am not like other people: thieves, rogues, adulterers, or even this tax collector. I fast twice a week; I give a tenth of all my income" (Luke 18:11-12).
There are three things wrong with this prayer. It is self important, self-righteous, self-justifying, and we all hate people who come under those three categories. Put them together, and you have a really awful prayer. Luke explains that Jesus "told this parable to some who trusted in themselves that they were righteous and regarded others with contempt" (Luke 18:9).
You can see that a heart full of self-importance, self-righteousness, and self-justification, makes any kind of genuine love impossible. Such a person can neither love God with all his heart nor love his neighbor as himself.
Do you know any self-important persons in this home or among your family and friends? All they care about is being treated with respect, and they assume that their needs and desires take priority over anyone else's. Jesus said that "all who exalt themselves will be humbled" (Luke 18:14), so it is a very dangerous situation to be in. We don't have to topple such people. God can be very tough with them in due course.
The self-righteous person is quite sure that he or she is good and all others are "thieves, rogues, adulterers" or greedy and cruel (that's what tax collectors were known for in Jesus'day). Such people can see the faults in everyone else, but they seem totally oblivious to what needs improving in their own character.
Self-justification is assuming that I am so good that I deserve every kind of blessing in this life and a very special place in heaven. In Jesus' day such people "trusted in themselves that they were righteous and regarded others with contempt" (Luke 18:9).
Now you can see that this kind of prayer makes us very unlovable, and makes it impossible for us to love others. Jesus contrasts that worst prayer in the world with the prayer of the despised tax collector. "God, be merciful to me, a sinner!" (Luke 18:13). What is so good about this prayer is that we admit we are imperfect like everyone else. We look to God to improve us. And in the words of the hymn "Nothing in my hand I bring. Simply to thy cross I cling."
That is what we express in the words of the prayer book confession.
"We acknowledge and confess our manifold sins and wickedness. We are heartily
sorry for these our misdoings. Have mercy upon us, most merciful Father,
and grant that we may hereafter serve and please thee in newness of life"
(the old Anglican Book of Common Prayer). And when we come to communion
we can say "We do not presume to come to this thy table trusting in our
own righteousness, but in thy manifold and great mercies." Notice the repetition
of the word "manifold." My many and various kinds of sin and shortcomings
are more than covered, and in due course changed into love, by the many
and various mercies of God.