What some saints have said about the importance of signing our bodies with the sign of the Holy Cross:
This sign is a powerful protection. It is gratuitous, because of the poor. Easy because of the weak. A benefit from God, the standard of the faithful, the terror of demons.” – St. Cyril of  Jerusalem (317-386)
Adorn and protect each of your members with this victorious sign and nothing can injure you.” – St. Ephraem of Syria (306-373)
When you sign yourself, think of all the mysteries contained in the cross. It is not enough to form it with the finger. You must first make it with faith and good will. When you mark your breast, your eyes, and all your members with the sign of the cross, offer yourself as a victim pleasing to God.” – St. John Chrysostom (349-407)
Let us not be ashamed of the Cross of Christ, but even if someone else conceals it, you must carry its mark publicly on your forehead, so that the demons, seeing the royal sign, trembling, may fly far away. Make this sign on all occasions.”– St. Cyril of Jerusalem
We adore you, O Christ, and we bless you, here and in all the Churches throughout the whole world, because by your Holy Cross, you have redeemed the world.