It is not clear where the teaching comes from but I have often heard that the word 'go' in the Great Commission is not the command. The supporting evidence given is this, the word 'go' is not in the imperative. Certainly grammatically the word 'go' is a participle so the imperative is not a choice. That may sound like an open and shut case, the word is not in the imperative mood so therefore it is not a command. While this is true that the word 'go' is not in the imperative, it is a participle, so what does that mean? In New Testament Greek (Koine Greek) the participle often has an enriching function in the sentence. One of the main uses of the participle is to combine two or more actions as a combined action. While we can't do this in English to the same extent as New Testament Greek can, if we say "he ran the ball to the end zone and won the game" we usually would think that the act of running the ball was how he won the game. This may be the case if something is simultaneously happening. In this use of the Greek participle, it has a tense that is expressed not in terms of the present, but in terms of the main verb. If the participle is present tense, it is the same time as the main verb. If the participle is past, it is sequentially before the main verb. There is still this fusing together of action to show unity in purpose, result, story, manner, or something.
So what if a participle is working with an imperative main verb. An example of that can be found in Matthew
"And he sent them to Bethlehem, saying, 'Go and search diligently for the child, and when you have found him, bring me word, that I too may come and worship him.' " -- (Matt. 2:8 ESV)
In this example Herod commands the Magi to search for the child. The word 'search' (ἐξετάσατε) is in the imperative, but the word 'go' (πορευθέντες) is an aorist participle. The aorist is often past action (sometimes simple action), and in this instance action that will precede the imperative. While the main idea is that the Magi are commanded to 'search' but in no way should one think that they have choices as to whether they should go to Bethlehem or not. The aorist participle is used to show what they must do first, and then what they will be able to do second. The 'going' is necessary in order to accomplish the 'searching'. I don't think most people would argue that Herod is not commanding the Magi to go to Bethlehem.
When Jesus tells us to make disciples in Matthew 28:19,20, there is not one but three participles. The first participle is 'go' which tell us what we have to do in order to do the main command. The main command is 'make disciples'. Then there are two other participles; 'baptize' and 'teaching'.
When I've heard this teaching that the 'go' is not imperative it seems to have the general thought that we are not accountable to go in order to fulfill the Great Commission. The idea seems to be that we can fulfill the Great Commission by staying where we are currently located. Certainly there is ministry to be done wherever we are. However, this is a misguided approach to the passage. Going is a part of the main action by setting up the circumstances through which the main command is to be accomplished just like the Magi had to go to Bethlehem in order to find the child.
Would we think that the ideas of baptizing and teaching are optional components to fulfilling the Great Commission? I would propose that what Jesus is telling us how we are to make disciples, we make by disciples by baptizing and teaching.
Go is a part of the full command of making disciples in the Great Commission. We are to do this. We might do it in many ways. The New Testament shows us how the first century disciples carried out this command. We are to go and make disciples. We make disciples by baptizing and teaching. Brothers and sisters, let us go and make disciples.
And Jesus came and said to them, "All authority in heaven and on earth has been given to me. Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all that I have commanded you. And behold, I am with you always, to the end of the age." -- (Matt. 28:18-20 ESV)