One might refrain from such but still harbor bitterness and ill will. We can tell what forgiveness is by observing what God does when He forgives. Forgiving one another is no more non- essential than baptism and the Lord's Supper. The example of Jesus urges it. We follow his example in being baptized, in eating the Lord's Supper, in attending worship services, etc.
Hate is the preventive to forgiveness.
The parable of the unmerciful servant illustrates this point. These verses relate one of the flatest statements in the Bible. It is a 'take it' or 'leave it' proposition. The most expensive thing in the world you can do is harbor ill will toward another. You have paid the price of the loss of heaven.