Rav Shlomo of Bobov zy”a (quoted in Gilyon Pri Hakerem, Gilyon 22) related that when he was 8-years-old, his mother once served him cabbage for supper. He did not like this food and refused to eat it, no matter how much his mother tried to convince him.
When his father, the Kedushas Tzion zy”a, heard about this, he told his son, “You should know that fruits and vegetables often contain within them a ‘nitztutz’, a spark of holiness, that can be uplifted when a Jew makes a bracha on them. Sadly, the majority of them do not make it to a Jewish table, and even more sadly, the minority that do make it to a Jew’s table often are consumed by people who do not make brachos properly.
“This cabbage was fortunate enough to make it to the table of an upright Jew who knows how to make brachos. How could you not make a bracha and eat it, and thereby uplift the nitzutz trapped within it?”
The Kedushas Tzion then told the Rebbitzen that from then on, she should serve cabbage for supper every night for a full year in order to train their son to eat whatever food Hashem sends his way and, by doing so, to uplift the spark of kedusha within the food.
