At it's most basic symbolic level, the Cross is an intersection. In fact, in Christ crucified we contemplate the intersection and coincidence of all opposites. The divine is joined to the human, our time-bound world coincides with the eternity of God, and the impassible God suffers his Passion. As an instrument of death, the Cross becomes the Tree of Life. And this is the same Tree of Life from the garden of Eden and the same Tree of Life from the New Jerusalem in Revelation 22. Thus the end is joined to the beginning and creation is restored to "original blessing."
Christ crucified proclaims to us, "I am the first and the last, the Alpha and the Omega, the beginning and the end."