The eyes of Mary, the baby, Catherine, and a page boy at her right are all fixed on the ring, which is the focal point of the painting, yet it does not stand out very clearly. Much more significant is the palm branch that the angel above is bringing to Catherine. A symbol of martyrdom, it serves as an explanation of what marriage to Christ entails. The red fabric to which the palm branch points expresses the same idea, red being the color of blood and of the vestments worn on the feast days of martyrs. In the legend Catherine will in fact die a martyr for the faith.
From the 15th century until around the time of this painting, images of the child pictured him naked as here. In the later 16th artists often used a piece of cloth or the mother's hand to get his genitals covered.
The Golden Legend says Catherine was "of the noble lineage of the emperors of Rome," and she is almost always pictured with a crown. In this case, Veronese has also given her a gown fit for a queen. As in most images of virgin martyrs, her hair is blond.
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Read more about images of the Mystical Marriage of St. Catherine of Alexandria.