We are called to action in our bitterness and anger according to Scripture. Scripture instructs us to get rid of it by showing kindness and compassion based on the way God forgives us. He does not withhold His kindness and forgiveness until we are perfect people. He blesses His children even while we are still sinning against Him. Our forgiveness towards others cannot be based on their past, present or future performance. God gives us daily grace when we have done nothing to deserve it.
As Scripture states, by not taking action to get rid of our unresolved anger we run the risk of causing grief to God's Spirit. Freedom from self is one of the most liberating freedoms we can ever experience. I should know...I am still in the process of becoming liberated!