"Amazing Grace" is a Christian hymn

Hymn

A hymn is a type of song, usually religious, specifically written for the purpose of praise, adoration or prayer, and typically addressed to a deity or deities, or to a prominent figure or personification...

 with words written by the English poet and clergyman John Newton

John Newton

John Henry Newton was a British sailor and Anglican clergyman. Starting his career on the sea at a young age, he became involved with the slave trade for a few years. After experiencing a religious conversion, he became a minister, hymn-writer, and later a prominent supporter of the abolition of...

 (1725–1807), published in 1779. With a message that forgiveness and redemption are possible regardless of the sins people commit and that the soul can be delivered from despair through the mercy of God, "Amazing Grace" is one of the most recognizable songs in the English-speaking world.

Newton wrote the words from personal experience.