We are all well aware that faith is required to move mountains and at least some churches are very quick to remind us that it is the prayers of a righteous man that are effective. Yet here in Mark 11:25&26 the Lord states quite bluntly that at least prayers for forgiveness are only effective insofar as we have already forgiven other people.
It is very interesting how the commentators handle this verse. Three of them skip the warning completely and discuss whether standing or kneeling are better prayer postures. Most of the rest water down the wording and suggest that a kind and forgiving nature and attitude is necessary for prayer to work. One limits the application of this verse to the exercise of vengeful miracles; referring back to the fig tree as context. Only Robertson goes as far as to suggest that God's willingness to forgive us is directly limited by our willingness to forgive others. He proceeds to note that this is a solemn thought.
I suspect the reason for the reluctance to take this verse at face value is the apparent clash with the notion of free grace. An important plank of protestant thought is that salvation and freedom from sin comes from repentance, that it is a free gift and that it is given to us despite our state at the time. Thus the notion that a work on our part is a necessary predicate upon forgiveness is anathema.
I suggest that this seeming problem is resolved simply by distinguishing the sinful nature from the sinful act. Romans 6&7 discuss this division at length but for me it is captured succinctly and personally by Romans 7v22-24. As believers fully saved by the free gift of repentance we delight after the law of God and have a home in heaven. Yet as human beings still upon earth; 24/7 reality tells us that we still do and think things that we shouldn't. Some choose to distinguish this by saying SIN (singular) for our inherent sinful nature and SINS (plural) for the day to day knocks and scrapes that happen even once sin has been dealt with. Doing this allows us to take these verses at full face value and simply learn their very simple message.
In the disciples prayer of Matthew 6 we find that immediately after asking for daily bread the Lord tells them to ask for forgiveness as they have forgiven those that have sinned against them. Just in case that didn't sink in the first statement after the prayer was to repeat that if they wanted their daily sins forgiven then first they have to forgive others. In fact the Lord had already taught that freewill offerings to God were invalid if you still harbor anger towards a brother internally. Paul continued in his letters to remind believers that mutual forgiveness was a cornerstone of church management and that it was to be based upon the fact that they had been forgiven through Christ.
I firmly believe that church life in general and my life in particular would be completely changed if we could fully get hold of these verses. Most 'full time' believers realize that they need to confess sin to God as part of their daily walk. But to understand that if we are still angry at Bob for something he did 5 years ago then the intervening 1585 days of sin confession was a complete waste of time is mind blowing. As we go forward from hear may we each remember the second half of the verse we have probably known since we were five: Forgive us our debts, as we forgive our debtors.