In the second assurance, the Buddha postulated a scenario contrary to his experience—one where there is no rebirth and no karmic retribution. He did this so that those who were doubtful could still benefit from his teachings.
He showed that even within such a scenario, one who remains free of greed, anger, and their resultant suffering will be truly happy!
Today, this assurance is especially helpful as people ask if they have to accept the existence of rebirth before they can benefit from the practice. As the Buddha showed, they do not have to accept rebirth in order to reap the benefits. Those who are free of greed, anger, and their ensuing suffering have a mind of loving-kindness, compassion, appreciation, and equanimity in this lifetime.
They no longer experience greed, no longer crave the emotional high from acquiring that which is new—they simply appreciate what they already have. Craving and its shadow, disappointment, are eliminated as people become contented with their situation. This is true happiness.
We can only imagine how wonderful it would be to never again crave sensations and experiences—to appreciate what we already have.
And imagine never again feeling angry or unsettled but always feeling calm and peaceful instead. Such a person would surely always be happy and be at ease, and thus always be welcomed wherever he or she goes. Without craving and without anger there will be no suffering—just happiness, a lifetime of happiness. And all this can happen here and now, because even if one does not believe in rebirth, one will still benefit if one lives a life free of craving, animosity, and unhappiness.