Justice: God is a just God, that's what we saw the king did for the debtors.
Grace is open to all that seek for it as Jn 1:16 says, the fullness of Jesus grants all grace upon grace.
Greed is a deadly enemy of the cross. This had caused standing believers to fall spiritually, physically and gracefully. We must seek His kingdom and His righteousness to overcome Balaam's, Gehazi and or Judas Iscariot's vicious greed.
Unforgiveness is a character of the unbroken. The servants did extended same mercy the granted to others, hence, he merited the judgment of the king. The Lord's prayer taught every true believer to forgive as to be forgiven.
Apostle Paul wrote to the Corinthians church in chapter 11 verse one, that, we must be imitator of Christ. He (Jesus) is the all compassing standard to all true disciple.