It’s the feast of the Exultation of the Cross.
It’s amazing to see through Scripture the types of the cross. At the beginning there is the Tree of Life in the Garden. The Tree of Life has stayed in the human pysche since the Fall to such a degree that most cultures have a tree of life myth of some sort.
Adam was supposed to take his bride and cling to the tree of life when Satan came, but he ate the other fruit instead.
In the desert the people of Israel sinned, putting God to the test and were punished with the poison of snake bites. To heal them Moses obeyed the command to make a bronze serpent and put on a stick so that all the people could look on it and be healed.
Finally the prophecies are fulfilled when Christ makes the cross the Tree of Life and He if lifted up with all our sins, like the bronze serpent, so that when we look on Him in His tortured body, we know we can be saved.
From Divine Office today:
Hail, O cross, consecrated by the Body of Christ, whose limbs, like precious jewels adorn your wooden timbers. Through you the world is redeemed by the blood of the Lord.