The Sacred Heart of Jesus is a very popular Catholic devotional image and it consists of several symbols. The Sacred Heart Medal is to remind us of the Passion of Christ on the cross hence the crown of thorns. But why the flames atop the heart? There are 3 reasons: 1) Christ’s sacrifice on the cross is the perfect consummation of all the sacrifices of the Old Testament, 2) in the Old Testament fire is associated with God (think Moses and the Burning Bush), and 3) the flames represent Christ’s burning love for us.
A traditional symbol associated with the Sacred Heart is rays of light surrounding the Heart. In John 8:12, Christ declares that He is the “light of world.” Light, like fire, is a symbol of divinity.
Another symbol is the crown of thorns, which encircle the Sacred Heart. The crown of thorns indicates that Christ felt His wounds in His heart. Our sins are the thorns pressing into Him. Also, after the resurrection the crown of thorns are a sign of victory of love over hate and life over death.