This touching background music "amazing grace" is a hymn.
This is a hymn written in18th century. The author was originally a slave captain, and this is his work when he turned over a new leaf and became a priest. This song is full of the author's remorse for his past slave trade, and gratitude to the God who blessed him despite these.
Grace originally meant "grace and grace", and here it is interpreted as "God's mercy and grace to mankind".