Jesus’ words are a warning against hypocrisy. It would be hypocrisy to ask for God to forgive us while harbouring resentment towards others in our heart. If citizens of the kingdom ask God for forgiveness, they cannot withhold forgiveness from others. Just as it is in the character of God to forgive his children, it is in the character of God’s children to also forgive others.1
15 but if you do not forgive others their trespasses, neither will your Father forgive your trespasses.