St. Peter Chrysologus
Squirrels never give birth to dolphins. Dolphins never give birth to possums. And humans never give birth to oak trees. Like produces and re-produces like. Old School Aristotelian and Thomistic philosophy – the basic intellectual structure of Catholicism – teaches us that this is b/c squirrels, dolphins, possums, and oak trees have a nature. That which makes a thing the kind of thing it is. Knowing a thing's nature tells you what it is and its telos, its end, or why it is. The nature of the human person is rational animal. To be a thinking, deliberative, and therefore, moral animal. When our nature is perfected, we only make moral choices that advance us toward our end – God Himself. The fruit we bear is the fruit of righteousness made possible by the grace of God and our free cooperation. Without God's grace, our fruit is rotten. Without Him, we can do nothing good. Jesus says, “. . .every tree is known by its own fruit.” Fig trees produce figs. Oak trees produce acorns. By nature, rational animals produce other rational animals. But it is only by cooperating with God's grace that we as rational animals make the good choices that lead us back to God.
But why should we cooperate with God's grace? Paul writes to the Ephesians, telling them that God – “who created all things” – has a “plan of mystery,” one hidden from the past, a plan Jesus was sent to reveal in the light for all to see. Those who receive this revelation of God's mysterious plan are collected together and called “the Church.” And it is the telos of the Church to preach and teach God's plan to the world, so that the “the inscrutable riches of Christ” might be made known. The first of these riches is a “confidence of access [to the Father] through faith in [His Son].” We should cooperate with God's grace not only to have access to the Father but also b/c doing so repairs our fallen nature and makes it possible for us to make those choices that bring us closer to our end – eternal life in the Blessed Trinity. Like produces and re-produces like. Good works done in grace produces and re-produces good works done in grace. Good works done in grace give glory to God. Thus bearing witness to His help and further revealing His plan for mankind. This is how and why we preach and teach. This is according to the eternal purpose accomplished in Christ Jesus.