For by grace you have been saved through faith. And this is not your own doing; it is the gift of God, not a result of works, so that no one may boast. (Ephesians 2:8,9 ESV)
Religion
Humans have developed many religions. Once society (and individuals) reject the truth of the One True Living God, ideas develop to fill the gap. Lots of humans, lots of religions.
Normally, such religions attempt to explain the unknown. Such religions attempt to give peace of mind. Such religions attempt, even, to draw near to the divine.
When Christ came, in fulfilment of all of God’s intentions and promises, He was not making a religion like those. He came as the One True God Himself, providing actual understanding, actual peace, and the only way to draw near to God.
All of this was upside down to what was common.
But particularly, Christ showed that the only way for anyone to draw near to God was for God to come near to us.
We draw near to God not by our efforts, but by God’s grace. And that was so very different. It requires humility rather than human achievement. It requires trust rather than human wisdom. It requires Christ, not our own heroes.
Grace turns the religious world upside down.