Turn the other cheek
Here’s what it means
Do not answer personal insult or mistreatment with revenge; be willing to absorb wrong rather than mirror it.
Why the Bible says it this way
The writer deliberately uses very strong language to make an important point. The point is serious even though the wording is not meant literally.
A helpful detail: The saying forbids personal retaliation and presses costly love. It should not be used to erase all biblical duties to protect others, tell truth, or pursue lawful justice.