Today we celebrate the exaltation of the Cross.
The Church is fond of comparing the Cross to a tree, especially the tree of knowledge in paradise. In support of this we may first of all cite the words of the Preface for Mass: "It was Your will that from the wood of the Cross our salvation should go forth. From a tree came death, from a tree also should come forth life. He who triumphed on a tree (i.e., the devil) should also be defeated on a tree. "
There are passages in which the liturgy gives evidence that the Sign of the Cross has sacramental efficacy. the sign of the Cross puts the devil to flight.
from The Church's Year of Grace by Dr. Pius Parsch