We are required to forgive all offenses, because if we can not forgive others, then Christ can not forgive us.
6:12 And forgive us our debts,
as we forgive our debtors.
forgive: hiēmi (to send; an intensive form of εἶμι eimi (to go)); to send forth, in various applications: - cry, forgive, forsake, lay aside, leave, let (alone, be, go, have), omit, put (send) away, remit, suffer, yield up.
debt: something owed, that is, (figuratively) a due.; morally a fault: - debt.
debtors: an ower, that is, a person indebted; figuratively a delinquent; morally a transgressor (against God): - debtor, which owed, sinner.
6:14 For if ye forgive men their trespasses, your heavenly Father will also forgive you:
trespasses: a side slip (lapse or deviation), that is, (unintentional) error or (wilful) transgression: - fall, fault, offense, sin, trespass.
6:15 But if ye
forgive not men their trespasses,
neither will your Father forgive your trespasses. This is whether they ask or not. We still have to forgive. Just like when Christ died on the cross, He forgave all sin, or else He would have to keep going back to the cross. So too we must forgive all trespasses against us.
If we try to limit our forgiveness only to those that ask for forgiveness for a particular trespass, then so too must Christ on forgive only those sins we ask for... and if that is the case... you had better not forget even just ONE!