Lords Prayer. Asking for Forgiveness

For those who beleive in the doctrine of **O**nce **S**aved **A**lways **S**aved (OSAS). How does one reconcile our need to not only confess our sins, but to ask God for forgiveness for those sins? > Forgive us our trespasses as we forgive those who trespass against us Some might say that in Mathew 6 the word should be translated as "debts" which are not necessarily "sins." Yet the parallel passage in Luke 11 uses the word "ἁμαρτία" which clearly speaks of sin. Question: If we have received forgiveness in full, and it is completed as many would suggest, why would the Lord have us petition (Pray) for our forgiveness when it has already, according to the OSAS doctrine, been freely given and can never be taken away? This question are for the Faith Practices that adhere to 'assurance of salvation' which includes most but not all the ecclesial bodies that broke and continue to break away from the Catholic Church.