According to tradition, St. Patrick wrote this prayer in the year 433 A.D. for divine protection before successfully converting the Irish King Leoghaire and his subjects from paganism to Christianity. The following is a short extract.

Christ with me,

Christ before me,

Christ behind me,

Christ in me,

Christ beneath me,

Christ above me,

Christ on my right,

Christ on my left,

Christ when I lie down,

Christ when I sit down,

Christ when I arise,

Christ in the heart of every man who thinks of me,

Christ in the mouth of everyone who speaks of me,

Christ in every eye that sees me,

Christ in every ear that hears me.

This prayer is called "St. Patrick's Breastplate" because of those parts of it that seek God's protection. It is also known as "The Deer's Cry" or "The Lorica". "...and having on the breastplate of righteousness;” (Ephesians 6:14). Paul compares our Christian armor to armor the Ephesians would have been familiar with, that of the Romans. A Roman breastplate was a metal shield of sorts that strapped on and guarded the soldier’s chest. Within the chest lies our heart. When our heart stops beating we die. Thus, the heart is a key target that an enemy will try to hit to end our lives. Our heart is also symbolic as the home of our spirit. The breastplate we are given to protect our heart is righteousness. Not our righteousness; but Christ’s. We have already gotten God’s approval, He sent Christ to be righteousness for us. No trick or scheme of Satan can take away that righteousness unless we let down our breastplate and bare our heart for him to take. By holding the sacrifice of Christ against our heart as a breastplate, we cannot be lost by attack to the heart.