John Newton (1725–1807) wrote Amazing Grace to celebrate his conversion from being a supporter of slave trade. John was on board a slave ship on May 10, 1748, returning home during a storm, when he experienced a “great deliverance.” In his journal, he wrote that the ship was in grave danger of sinking. He exclaimed “Lord, have mercy upon us!” He was converted, though he continued in the business of slave trading. Many years later, he left the slave trade, eventually became a minister in the United Kingdom, and spoke out against it.
A typical slave ship would leave port with 600 slaves. They were kept in irons and horrible conditions for the entire voyage. By the time the ship arrived, only 200 slaves would be alive, the rest having died of dysentery and other disease contracted on the ship. Out of these wretched and hellish, conditions a beautiful song was born.
http://en.wikipedia.org/wiki/Amazing_Grace
Amazing Grace, how sweet the sound,
That saved a wretch like me
I once was lost, but now am found,
Was blind, but now I see.
‘Twas Grace that taught my heart to fear,
And Grace my fears relieved;
How precious did that Grace appear,
The hour I first believed!
Through many dangers, toils and snares,
We have already come;
‘Tis grace hath brought me safe thus far,
And Grace will lead me home. (Lead me home!)
The Lord hast promised good to me,
His word my hope secures!
He will my shield and portion be,
As long as life endures.
Yea, when this heart and flesh shall fail
And mortal life shall cease,
I shall possess within the veil
A life of joy and peace.
The earth shall soon dissolve like snow,
The sun forbear to shine;
But God, who called me here below,
Will be for ever mine.