The Bible
All Scriptures are given by inspiration of God (2 Timothy 3:16-17), and they provide us with everything needed for life and godliness (2 Peter 1:3).
The Old Covenant or Law of Moses was fulfilled by Christ (Matthew 5:17) and nailed to the cross (Colossians 2:14), and we are now to live by the authority of the New Covenant or Law of Christ (Hebrews 8:6-13; 9:15-17; 1 Corinthians 9:21).
Everything we teach and practice (Colossians 3:17) must be based upon what the perfect law of liberty has revealed to us (James 1:25).
If we preach a different gospel than the gospel of Christ we will be accursed (Galatians 1:6-9).
We must abide in the teachings of Christ to have fellowship with God and His Son (2 John 1:9), and therefore must not add or take away from God’s Word (Revelation 22:18-19).