St. Augustine, Why is Prayer not an Optional Thing?

Question 018.

In other words, prayer is not an extra, but is a part of the fulfillment of our nature?

Man is the image of the one whom he is capable of enjoying, and whose partner he can become…man has been created in such an excellent state that even although it is itself mutable, it reaches happiness by cleaving to the unchangeable good; that is, to God. Nor can it satisfy its need unless it is totally happy; and only God suffices to satisfy it.

from St. Augustine Answers 101 Questions on Prayer by Fr. Ermatinger.

While it is true that the things of creation have ends according to their natures, man quickly finds that seeking an end according to a created nature is elusive, illusionary, and ultimately dissatisfying if arrived at. A veritable garden of earthly delights delights not and length of years but weariness and length of misery. As man progresses inward, going into the inner chamber of his heart, and shutting the door, seeking to commune with his ineffable Creator, he finds that, as he grows in the life of prayer, he increasingly begins to not pray for the obtainment of created things as an end unto itself. Rather, his desire is drawn ever upward, changing and growing in the Divine Light, to pray for supernatural things; that he might be in closer communion with God, and that those for whom he prays also enjoy such communion. It is not that his heart grows disinterested in created things, but disinterested in created things as ends for himself. God alone suffices and created things are viewed as means, either taken up or left behind, to further that supernatural destiny that is imprinted upon his nature and inflames his heart the more it is sought.

— PPP