precious: worth a great deal, and so costly, rare, or highly prized.
At its heart this word measures worth. Something precious is worth a great deal, and everything else the word says grows out of that one idea.
Because a thing of great value usually costs a lot, the word most often describes expensive materials: gems, fine building stone, gold, and the treasures a king stores up. Because a thing of great value is often hard to come by, the word can also mean rare or scarce, as when a message from God was in short supply. And because worth is not only about money, the word reaches into what people treasure: a life, wise words, love shown by God, or a person held dear. In each case the sense of high value carries over, whether the price is counted in silver or in the heart.
So the same word can label a diamond, a scarce word from heaven, and a beloved child. English needs several words to follow it (costly, rare, prized, splendid), but in the original they are all one word turning to face different things that are worth much.