"The Great Commission"...?

When you hear most people preach or speak on the topic of "the great commission", it starts here at Matthew 28:18 and it continues through 20. 18. And Jesus came and spake unto them, saying, "All power is given unto me in heaven and in earth. 19. Go ye therefore, and teach all nations, baptizing them in name of the Father, and of the Son, and of the Holy Ghost: 20. Teaching them to observe all things whatsoever I have commanded you: and, lo, I am with you always, even unto the end of the world. Amen.
If you have been to any church between 1862 and now, then you've probably heard the phrase, "the great commission", being used by preachers, speakers, and church leaders throughout the world. While these three scriptures are used to form a foundational teaching or doctrine(belief system) within the so called "christian church", it's the two scriptures preceding these that are often left out that, I believe, are necessary to form the correct teaching(sound doctrine). Matthew 20:16-17 says, Then the eleven disciples went away into Galilee, into a mountain where Jesus had appointed them. And when they saw Him, they worshiped Him: but some doubted. 
And it's not just those preceding scriptures that must be read but the "The Acts of the Apostles" and ever other book following. Also, I would venture to say, every word preceding those two verses going back to Genesis. I mean, nowhere in the Old Testament of the Holy Bible, does any prophet give the indication that the instruction of the Son of God would be for EVERYONE that calls on and believes in Christ to become a preacher and or teacher of God's Word(the gospel). You do realize that EVERYTHING Jesus did and taught was foreshadowed and spoken of before He came into the world. And EVERYTHING He taught and did was retaught or reiterated by His chosen preachers(apostles). And at no time did His apostles teach that everyone had a mandate to preach nor teach the gospel to every nation. In fact, what they did preach and teach, in that regard, is to live a life that is holy so the world would SEE it and desire to have the same. Amen.