Centuries before our time, Cicero derives religion this way:
Those who carefully took in hand all things pertaining to the gods were called religiosi, from relegere [careful consideration]. Such reverence is in keeping with the Roman reverence for tradition followed by the whole community to ensure health and prosperity.
We are tied to God and bound to Him [religati] by the bond of piety [right dealing towards the gods], and it is from this, and not, as Cicero holds, from careful consideration [relegendo], that religion has received its name. Not just careful behavior, but a bond and not to your city or your tribe, but to God and not optional either. We are bound by nature. To be religious is to look above now. And this change in attitude is not confined to Christians. It’s in Plotinus and later Platonists too.
Augustine dresses this upward gaze with the very Christian conception of recovery:
having lost God through neglect [negligentes], we recover Him [religentes] and are drawn to Him. But he later returns to Lactantius’ more elemental derivation.
This fourth century sense of religion, being of God, being apart from the world survives today, whether talking of Rome and the Christians or society’s persecution or bemoaning religious talk outside of church. As used today, Religion no longer means reverence for this world’s things, despite calls from the dark.