Matthew 28:20 Teaching them to observe all things whatsoever I have commanded you: and, lo, I am with you alway, even unto the end of the world. Amen.

John Gill Commentary:

whatsoever I have commanded you; 

every thing that Christ has commanded, be it what it will, and nothing else; 

for Christ’s ministers are not to teach for doctrines the commandments of men; 

or enjoin that on the churches, which is of their own, or other men’s devising, and was never ordered by Christ;

John 17:17 Sanctify them through thy truth: thy word is truth.