A breastplate is a type of armor and usually a metal plate which is used for defense of the chest. A breastplate is also something worn in ancient times by the Jewish high priest which had twelve gemstones and the names of the tribes of Israel.

Positive: Seeing a breastplate in a dream could represent defense, royalty, or righteousness. It could symbolize putting on the armor of God and being prepared for battle.

Negative: Dreaming of a breastplate could represent a warning about an upcoming spiritual battle. If you see a cracked or broken breastplate it could represent not being properly prepared for battle.

(Ephesians 6:14).