Discipline exposes your child's inability to love his sister from his heart, or genuinely to prefer others before himself.  Discipline leads to the cross of Christ where sinful people are forgiven.

The alternative is to reduce the standard to what may be fairly expected of your children without the grace of God.  The alternative is to give them a law they can keep.  The alternative is a lesser standard that does not require grace and does not cast them on Christ, but rather on their own resources.

Many parents get confused at this point.  They realize their children are unable to love others from the heart without salvation and new birth.  So they conclude that, since it is not possible, the standard must be lowered.  They set a standard that is in keeping with their children's resources.

Dependence on their own resources moves them away from the cross.  It moves them away from any self-assessment that would force them to conclude that they desperately need Jesus' forgiveness and power.

I have spoken to many parents who feared they were producing little hypocrites who were proud and self-righteous.  Hypocrisy and self-righteousness is the result of giving children a keepable law and telling them to be good. To the extent they are successful, they become like the Pharisees, people whose exterior is clean, while inside they are full of dirt and filth.  The genius of Phariseeism was that it reduced the law to a keepable standard of externals that any self-disciplined person could do.  In their pride and self-righteousness, they rejected Christ.