You are asking about one sentence—"So the servant fell on his knees, imploring him, 'Lord, have patience with me, and I will pay you everything.’"—which is part of the Parable of the Ungrateful Servant (Matthew 18:23-35). As a moral directive it is, as you note, about the importance of forgiveness in all situations. The servant owes his master 10,000 talents—a huge amount that he cannot pay. Under the law, he and his wife and children would all be sold into slavery to repay the debt. But in response to the sentence you cite, the master takes pity and forgives him the entire debt. The same servant later meets another servant who owes him a small amount and, when he can't immediately repay it, has him thrown in prison. When the master hears of it, he angrily castigates the servant for his lack of mercy and sends him to prison until the debt is repaid.
At a deeper level, what I find in this parable is an explanation of the question of karma. There is certainly a karmic law that holds us accountable for the consequences of our negative choices—just as there is a clear law in the parable concerning the repayment of debt. But karmic law is not a spiritual absolute—it can be dissolved in an instant by the infinite Love that is God, so long as we are willing to acknowledge the debt and request the mercy.
But we can't exempt ourselves from karma and then impose it on others—or on other aspects of our own consciousness. The ungrateful servant experiences the negative energy of karma, not because it is imposed from above, but as a result of his own choice. If we are to live in the constant flow of divine grace and love, then we must express that grace and love at every opportunity, and in the face of every challenge. We are only subject to the limiting law of karma if we insist on applying it—to ourselves, and to others. The alternative—freely available—is to live as clear channels for the infinite Love that is infinitely available.