There would be a lot of things different in this world if we had no disagreements, but we are all sinful people and this is the life we must live until the end of this age.
In my sinful condition, I struggle with relationships from time to time and need to be reminded of what the Bible says about things like bitterness and anger. We cannot be fooled into thinking that it is “all right” to be this way, as if somehow another’s misstep has given us license to “bare our teeth,” so to speak. It is a dangerous thing to be unforgiving or bitter. A while back, I heard John Piper answer a question concerning these issues:
(U)nforgiveness is a hell-bent sin. The Bible says that if you do not forgive those who sin against you, God will not forgive you (Matthew 6:15). In other words, this is a mortal issue. An ongoing, unforgiving, bitter, and angry spirit will kill a person’s heart, making them shipwreck their faith and prove that they never belonged to God. God is showing you how serious this sin is.
This means that now you have the potential of saying, “If he loves me still, and he forgives this, it’s like forgiving the apostle Paul!” (It’s like forgiving murderers, because the Bible says that if you hate your brother you’ve killed him [Matthew 5:21-22]). And then maybe the emotional transaction of forgiveness and justification would so overwhelm you that the resources that you do not now have for loving this other person would be given you out of that fresh, new experience of grace.
We can’t choose to just live with these things in our heart. They don’t just sit there, but rather fester and poison everything around them. It’s not healthy, and in fact is deadly.