The traditional Jesuit portrayal of the first three Greek letters of the name of Jesus is in the center. The star symbolizes the Virgin Mary; the flowers, St. Joseph. I am happy to credit the John Thavis blog for this information and for the image below (see my other post today for the link to his blog).
The Latin motto "miserando atque eligendo", which I translate "pitying and also choosing [him]," refers to the call of Matthew by Jesus. My grammatical suggestion for Latinists in the audience is an Ablative of Manner indicating how Jesus saw Matthew and thus leading to the famous command "Follow Me." My own personal interpretation is that the two actions of being merciful and of selecting are inseparable. Part of God's mercy is giving us a great and meaningful task and challenge in life.