The interior life for a Catholic means finding God in all things, leading to a life of contemplation in action.
Faith in Jesus Christ has consequences. A devout Catholic, who takes his faith seriously, will live in way that is in conformity with Catholic doctrine and morals. An atheist will lead a different kind of life since he sets his own norms. The Catholic who leads a serious interior life, and lives in accordance with the truth he knows, will be at peace with God, with himself and with his neighbor. He will also find a certain amount of limited happiness and joy because he has found purpose and meaning in his life.
The interior life for a Catholic means finding God in all things. Since God made everything that exists, and since every effect has a relationship to its cause and reflects the cause in some way, it follows that the fingerprints of God are on all things. The problem for many of us is that we are so taken with the beauty and goodness of the things around us, that we do not penetrate beyond those created things to the One who made them. St. Ignatius Loyola, the founder of the Jesuits, would fall into an ecstasy at night by looking at the stars in the sky, seeing in them the omnipotence, goodness and beauty of God. One of the goals of his interior life was to find God in all things.
The interior life leads to a life of contemplation in action. Action is required because we are social beings, put on this earth by God, to work out our salvation “in fear and trembling,” as St. Paul put it (Phil. 2:12).
There are many models of the interior life that we can strive to imitate. The most important one, of course, is the God-Man, Jesus Christ. He is our God, our Redeemer and our Teacher. His Gospel is the way to eternal life. But his interior life is mysterious and hidden from us, because he is a divine person and, therefore, incomprehensible to any created intellect, such as a human or angelic intellect. Therefore, the imitation of Christ can never be perfect.
After Jesus, we have the example of his Mother, the Blessed Virgin Mary. The Gospels do not tell us very much about her; they quote her six times. We know nothing about her childhood, and very little about her adult life—except that an angel appeared to her, she agreed to be the mother of the Messiah, and she gave birth to Jesus in Bethlehem. She appeared a few times in his public life, as at the marriage feast at Cana, and also at the foot of the cross on Calvary. Mary was a woman of faith, wrapped in silence. She was the first Christian, a perfect Christian. Mary did not fully understand Jesus (Luke 2:50) because no one can, but she pondered and meditated on what he said and did (Luke 2:19. 51). The interior life of Mary is the important fact about her; she was totally sinless and totally dedicated to God and to her Son, Jesus.
In the lives of the saints of the Church, we also encounter models of the interior life. St. Augustine of Hippo is one of the greatest. In his justly famous book of Confessions, he wrote down, for all generations, the amazing story of his interior life: his pilgrimage from a life of sensuality and pride, to conversion and dedication to Christ. Other saints who have written down and revealed the secrets of their interior life are: Teresa of Avila, John of the Cross, Ignatius Loyola and Thérèse of Lisieux. With the help of God’s grace, they developed an intense interior life that put them in contact with their own true selves, with others and especially with God, who makes his home in the soul of the justified, as Jesus says beautifully in John 14:23: “If a man loves me, he will keep my word, and my Father will love him, and we will come to him and make our home with him.”
Over the centuries—since Pentecost and the descent of the Holy Spirit on the Church, with the help of God’s grace and the guidance of the Church—millions of Christians have developed a truly interior life that brought them to explicit self-awareness and self-possession. We can do that also, if we use the proper means that are offered to us by divine revelation, by tradition, by the teaching of the Church and by the example of the saints.