It is an eternal spiritual law that we have to forgive: Jesus said that when we come to prayer, whatever it is that we are holding against another—lay it down. God will heal us. I speak of it as a healing because of the fact that when we are holding anger, it literally creates a state very similar to that of physical sickness. And it can come on suddenly. One day we are walking close to the Lord, and a situation arises and we become angry—and it may be an understandable reaction to whatever has happened, but we need to take that to the Lord quickly. If we allow it to linger and we literally feed the fire, it will not be long before we are unwell and unstable. We can recognize the feeling we have because it contrasts drastically with our previous state of mind: Whereas before we had a sense of peace, we now feel unstable and distanced from God, and probably confused. It isn't that God has left us, but we have allowed the anger to stand in our way. We may continue to make attempts to come to God in prayer, but as our mental and spiritual state worsens there is the danger that we won't feel we can. Of course, nothing could be further from the truth because we can always turn to the Lord.
Satan watches for situations like this because he knows how vulnerable we are in a state of unforgiveness. He will try every tactic he knows. This, dear friend, is a full-out spiritual battle.
During a time like this do not forget that Jesus said He has "all authority" in heaven and on earth. We can speak forgiveness, even if it does not feel real to us, but "Lord, here it is, take this from me. Forgive my anger and cleanse me from it." We should come to the Lord and give Him praise and speak words of faith regarding his love for us.
Anger is a trap we can fall into, but God will protect us. His Holy Spirit is with us and is the One who comforts us and guides us; Holy Spirit—Teacher, Comforter, Counselor. A prayer of the psalmist would include words such as "Lord, please forgive my sins and remember me with mercy," and certainly God does that for all of us if we will ask. Jesus' teaching about forgiveness puts it all into perspective as we gain understanding of the eternal laws of the Kingdom of God.