C.F.W. Walther says on Lam. 3.22-23:
"His mercies ... are new every morning." On earth, as long as a new morning follows the evening, those mercies never cease. Although God has shown mercy to the whole sinful human race for centuries, and although He follows each individual with mercy for many years, that mercy does not end. As human beings, we have a small amount of mercy and we all to soon reach the limit of our patience in dealing with our fellow sinners. If we have already demonstrated mercy toward someone several times, we deem that to be enough. If the one to whom we have shown mercy is ungrateful, if he uses that mercy against us, the fountains of our mercy toward him easily and quickly dry up forever. The fountains of divine mercy, however, flow continually and even the basest ingratitude and the most wanton misuse cannot stop them. This is a bottomless sea of love and it can never be exhausted.
-God Grant It, p15