A couple of things actually don't add up to me about Matthew 28:19.
1. How come the Gospels of Mark, John, and Luke that cover the same incident before the Ascension of Yeshua that describes the conversation we read in Matthew 28 is not listed in the other 3 Gospels?
2. How come we never see anyone being either [water or spirit] Baptized anywhere in the New Testament if that was the command of Yeshua?
Something just doesn't add up.
The NT did not begin until after Jesus' death, burial, resurrection and He was glorified and poured out the Holy Ghost at Pentecost.
All of the gospels give some details of Jesus final words regarding the Great Commission that would begin after He ascended back into Heaven:
Matt 28:18-20
And Jesus came and spake unto them, saying, All power is given unto me in heaven and in earth.
Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost:
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.
Mark 16:15-16
"Afterward he appeared unto the eleven as they sat at meat, and upbraided them with their unbelief and hardness of heart, because they believed not them which had seen him after he was risen.
And he said unto them,
Go ye into all the world, and preach the gospel to every creature.
He that believeth and is baptized shall be saved; but he that believeth not shall be damned."
In the Luke account Jesus prophesied that the gospel message would begin in Jerusalem and eventually go into all nations. That message would include his sacrifice and resurrection. And that repentance, and remission of sins was to be preached in His name. Clearly this is a reference to the message presented by Peter at Pentecost. (Acts 2:36-38):
Luke 24:46-49
"And he said unto them, These are the words which I spake unto you, while I was yet with you, that all things must be fulfilled, which were written in the law of Moses, and in the prophets, and in the psalms, concerning me.
Then opened he their understanding, that they might understand the scriptures,
And said unto them, Thus it is written, and thus it behooved Christ to suffer, and to rise from the dead the third day:
And that repentance and remission of sins should be preached in his name among all nations, beginning at Jerusalem.
And ye are witnesses of these things.
And, behold, I send the promise of my Father upon you: but tarry ye in the city of Jerusalem, until ye be endued with power from on high."
The last thing in the Book of John concerning the gospel message was Jesus instruction to Peter.
He was told to feed Jesus' lambs, and sheep as well as other sheep. Peter obeyed Jesus by presenting the gospel message to the Jews, (Acts 2:36-42) then assisting the Samaritans, who were half Jewish and half Gentile, to receive the Holy Ghost, (Acts 8:12-18) and presenting the gospel to the Gentiles as well. (Acts 10:43-48)
John 21:15-17
So when they had dined, Jesus saith to Simon Peter, Simon, son of Jonas, lovest thou me more than these? He saith unto him, Yea, Lord; thou knowest that I love thee. He saith unto him,
Feed my lambs.
He saith to him again the second time, Simon, son of Jonas, lovest thou me? He saith unto him, Yea, Lord; thou knowest that I love thee. He saith unto him,
Feed my sheep.
He saith unto him the third time, Simon, son of Jonas, lovest thou me? Peter was grieved because he said unto him the third time, Lovest thou me? And he said unto him, Lord, thou knowest all things; thou knowest that I love thee. Jesus saith unto him,
Feed my sheep.