I don't understand how 'the word of God' written later can supercede 'the word of God'?
We are under a new covenant. God’s ways of dealing with mankind have changed even though God Himself hasn’t.
But if you don’t understand that, you clearly are unfamiliar with the teachings of Christ and have not read much of the NT.
Read it. Go to church. A Christ centered church. Read Christ’s own words.