From Gregory the Great's Pastoral Rule:
For hence it is that the Church says by the voice of the elect, His left hand is under my head, and his right hand shall embrace me Canticles 2:6. The left hand of God, to wit prosperity in the present life, she has put under her head, in that she presses it down in the intentness of her highest love. But the right hand of God embraces her, because in her entire devotion she is encompassed with His eternal blessedness. Hence again, it is said through Solomon, Length of days is in her right hand, but in her left hand riches and glory Proverbs 3:16. In speaking, then, of riches and glory being placed in her left hand, he showed after what manner they are to be esteemed. Hence the Psalmist says, Save me with your right hand Psalm 107:7. For he says not, with your hand, but with your right hand; in order, that is, to indicate, in saying right hand, that it was eternal salvation that he sought. Hence again it is written, Your right hand, O Lord, has dashed in pieces the enemies Exodus 15:6. For the enemies of God, though they prosper in His left hand, are dashed to pieces with His right; since for the most part the present life elevates the bad, but the coming of eternal blessedness condemns them.