Augustine of Hippo was a 4th-5th century Christian theologian and philosopher. His writings have greatly influenced the development of Western Christianity and philosophy. Augustine is recognized as a saint in the Catholic Churches, the Eastern Orthodox Church, and the Anglican Communion and as a preeminent Doctor of the Church. He is also the patron of the Augustinians.
Augustine is the patron saint of brewers, printers, theologians, and a number of cities and dioceses. Among his most important works are The City of God, De doctrina Christiana, and Confessions.
The painting depicts the story of St Augustine and the seashell. Walking along the beach, Augustine saw a small boy using a seashell to pour seawater into a hole. The boy explained that trying to fit all the sea into that small hole was just as impossible as Augustine's challenge, trying to comprehend the complexity of the Holy Trinity with his small mind.
This painting was commissioned by Father James Cassidy for the church of St Augustine in Milton Keynes.
References from Wikipedia and Tradition In Action.org