Romans 14:23 tells us simply that anything that is not of faith is sin.  Faith comes from God. (James 1:17) Faith comes by hearing the word of God. (Romans 10:17) It is possible to read the Bible and not hear the word of God. (2 Corinthians 3:14) We must remain connected to Christ. (John 15:5) We can become disconnected. (Colossians 2:19)

Everything that doesn't originate from God is sin.