And when ye stand praying, forgive, if ye have ought against any: that your Father also which is in heaven may forgive you your trespasses.
Note 11 at Mr 11:25: Qualifications on believing and receiving are mentioned elsewhere in Scripture (see note 49 at Mt 7:7). This verse and Mr 11:26, which follow the often quoted Mr 11:23-24, also give restrictions on receiving answers to prayer. Un-forgiveness in our hearts will keep our prayers from being answered.
We should forgive others as quickly as it takes to make the decision to pray. The Greek word for "when" in this verse is "HOTAN," and it means "whenever" (Strong's Concordance). When we stand praying, we must forgive if we have "ought" (Greek - "EI TIS," which means "if any" [Strong's Concordance]) against anyone.
When we are offended or hurt, we often feel justified in holding a grudge. The Old Testament Law expressed this when it stated, "Eye for eye, tooth for tooth" (Ex 21:23-25). Until the offense was paid, those offended did not feel free to forgive. However, God dealt with everyone's offenses by placing sin upon the perfect Savior who was judged in place of every sinner of all time. To demand that others now earn our forgiveness is not Christlike. Jesus died for every person's sins (1Jo 2:2), extending forgiveness to us while we were yet sinners (Ro 5:8), and we should do the same (Eph 4:32).
It is doubtful that those who refuse to forgive have ever experienced forgiveness themselves. That would be comparable to the servant who was forgiven over $3 billion and yet refused to forgive his fellow servant who owed him $3,000 (Mt 18:23-34). The forgiveness that we have received from the Lord is infinitely greater than any forgiveness we could ever be asked to extend toward others.