Proverbs 31:8 Open thy mouth for the dumb in the cause of all such as are appointed to destruction.
9 Open thy mouth, judge righteously, and plead the cause of the poor and needy
These two verses are simply saying we need to speak up for those who are unable to speak for themselves. We are not to let the helpless just stand there and be punished because they cannot defend themselves. We need to be aware of their situation so we will be able to help them because of their conditions of weakness. The king was to righteously uphold the case of the helpless in physical and material crisis. The king thus meditates on the the compassion of God. We are to be ready in whatever case we find someone in to help them with the guidance and leadership of God, using the wisdom and knowledge we have gained.