The Corinthians can understand only easy truths like babies who can drink only milk. They are not mature enough to understand greater truths like older children who now can eat solid food. (See: [[rc://en/ta/man/translate/figs-metaphor]])
It is implied that they are not ready to understand more difficult teachings. Alternate translation: "you still are not ready to understand the harder teachings about following Christ" (See: [[rc://en/ta/man/translate/figs-explicit]])