How could john newton reconcile his christian faith with his career as a slave ship captain?

As a slave ship captain, John Newton would read passages from the bible and often used it as a basis to do punishment to the slaves.But over period of time, John Newton realized the devastating effects on Africans and started to take a stand against it. John Newton felt he had 'lost his way' in life for a time and that was the time while he was engaged in the slave trade. This led to his 'second life' career as a musician, poet, author and member of the Clergy of the Church of England. This events made him reconcile his Christian faith.