The round windows up high in the sanctuary are from left to right: a Chalice and the cross, a skull, the Immaculate Heart of Mary, a scale in the center, a harp, a dove with the olive branch and an ominous eye.  

Starting with the left, the chalice and the tilted cross behind it makes the connection between the chalice and what is in the chalice, the blood of Christ in the Eucharist. As Catholics, we believe that the host of unleavened wheat bread becomes the actual body of Jesus Christ when the priest prays those sacred words that Jesus said at the Last Supper. In saying these words, it is a living out of that first Mass ever celebrated by Jesus Himself as He said, “This is my body, given up for you.” Jesus said it, and so it is true, it really is His body. “In a similar way,” when the priest prays those words, “…for this is the chalice of my blood, the blood of the new and eternal covenant, which will be poured out for you and for many, for the forgiveness of sins…” Jesus said that it is indeed his blood in the chalice. We come up with long words to describe how this happens, but when it comes down to it, all we know is that if God says it, He can make it happen. Therefore, we know it to be true that after the consecration, the wine is no longer wine, but the blood of Jesus Christ himself. It does not taste like blood; it tastes like wine. We simply take it on faith in the words Jesus gave us.
The cross behind the chalice speaks of the crucifixion of the once and for all sacrifice. Though Jesus died for us about 2000 years ago, he is still present to us crucified in the Mass. So Jesus is not crucified over and over again. Jesus Christ crucified becomes present to us during Mass. This is the golden opportunity. Have you ever wondered what you would say to Jesus if you were able to be present to Him while He is dying for you on the cross? I would imagine thanking Him, praising His name and asking forgiveness for my sins and those whom I serve. I would ask Jesus to have mercy on as many people as possible. After all, it is in that moment that He offered Himself “for you and for many” to the Father for “the forgiveness of sins.”
The cross of Jesus and His chalice have become one. The cross was an act about 2000 years ago made present to us today in the chalice at Mass. It is an invitation for us to become one with Him. All this made present in the symbol of His crucifixion. But that is a much deeper meditation for another day.