There were three crosses on Calvary that Friday. The outside crosses held thieves and justice was being upheld. The figure on the center cross was being crucified because in Him, God had come and this was too disturbing to sinful humanity.
The thief on the right railed against Jesus, “… if thou be the Christ, save thyself and us.” But the other thief rebuked his partner in crime saying, “Dost thou not fear God, seeing thou art in the same condemnation? And indeed justly, for we have received the due reward of our deeds, but this man hath done nothing amiss.”
The thief turned to Jesus and pleaded, “Lord, remember me when thou comest into Thy Kingdom.” And Jesus said unto him, “Today shalt thou be with Me in Paradise.”
Note how the whole movement of the window is upward, through the central cross Jesus to the Father. The seed shape of the Chi Rho under the central cross represents the Tomb of Burial of Jesus.