We need strict judgment because it keeps us in line and if there were extra Divine favor and mercy then we would lose out on the great benefits of strict judgment. However, the Jews who make a bracha even on small amounts of food – above and beyond the letter of the law, achieve the same benefits when shown mercy. There is no danger that they will veer from the path because they are so intent on finding and appreciating chesed Hashem.
The greatness of the Jew is that he thanks Hashem even for small amounts.
When a person receives Divine favor of which he is not deserving, he is liable to feel that there is no value in doing the right thing because he is rewarded even when he doesn't do the right thing. However, a person who is inculcated with a strong feeling of gratitude will only do what is correct and moral even when he is the beneficiary of extra chesed. Such a person is not going to rebel when he sees how good things are despite his own inadequacies. That he possesses the quality of being faithful is proven by the fact that he thanks Hashem for a small amount of food, even though he remains hungry. This enables him to be the recipient of Divine favor.
To summarize the 2 ideas: We have the concern that when foregoing strict judgment a person will not receive its benefits and an additional concern that he will incorrectly think that it doesn't pay to do what is right. These two concerns are overridden by his great feeling of gratitude expressed by making a bracha over a small amount of food.
לרפואת ר' נח בן חי' ליבא