Newton wrote the words from personal experience. He grew up without any particular religious conviction, but his life's path was formed by a variety of twists and coincidences that were often put into motion by his recalcitrant insubordination. He was pressed (involuntarily forced) into service in the Royal Navy, and after leaving the service, he became involved in the Atlantic slave trade. In 1748, a violent storm battered his vessel off the coast of County Donegal, Ireland so severely that he called out to God for mercy, a moment that marked his spiritual conversion. Whilst his boat was being repaired in Lough Swilly, he wrote the first verse of his world famous song. He did however, continue his slave trading career until 1754 or 1755, when he ended his seafaring altogether
He did not renounce working in the slave trade until later in his life. After his return to England in 1750, he made three voyages as captain of the slave ships Duke of Argyle (1750) and African (1752–1753 and 1753–1754). After suffering a severe stroke in 1754, he gave up seafaring and slave-trading activities. But he continued to invest in Manesty's slaving operations.