Why did Jesus ask His disciples to forgive the debt of their debtors (if they want their debt to be forgiven), if Jesus's atonement is universal?

In the Lord's Prayer (Matthew 6) Jesus Christ teaches His disciples how to pray and encourages them to "Forgive the Debt of Others" if they want "Their Own Debt to be Forgiven". Why would Jesus encourage His disciples to do this, if His own death will atone for **all** sins / debts: Past, Present, and Future? I welcome answers from all denominations. **Note**: When I said that I am interested in answers from all denominations, I meant what I said, which is to say that I am interested in the way each denomination values the importance of forgiving others.