It is a metaphor that things are so valuable that they would not be exchanged for gold.

Friends for a lifetime means that it is rare to have a few close friends in life! If there is such a person, cherish it. Things outside the body cannot buy people's hearts.

Similar words for "金不change": priceless treasure

Priceless treasure, a Chinese idiom, pronounced as wú jià zhī bǎo, refers to extremely precious things. From "Gift to the Neighbor Girl" by Tang Yuxuanji.

Idiom usage:

Formal; as an object; with a complimentary meaning.

Example:

The second fold of "Lichuntang" by Wang Shifu of the Yuan Dynasty: "My beaded dress is a priceless treasure."