This phrase is used to refer to someone, usually a woman, who is getting older and is still single, implying that she will never marry and will end up dressing saints, as done traditionally by unmarried women in churches.
Examples
- Spanish: María tiene 40 años y aún no se ha casado, parece que se va a quedar para vestir santos.
- English: María is 40 years old and still not married, it seems that she will end up dressing saints.