It means that words (including teachings and knowledge) may become meaningless if circumstances change.
It means that words (including teachings and knowledge) may become meaningless if circumstances change.
In modern days, it is often used to refer to untrustworthy words that are disregarded the moment the situation changes.
It comes from how words carved on ice are strong when they are in the same state as when they are carved (in low temperature), but when the environment changes, such as when the temperature rises, they melt away easily, leaving neither the ice nor the carved words behind.