The Great Commission was Jesus last instructions to His disciples. I believe this is one of the most confused of all Jesus commands. I personally take this command as making disciples of all nations, which doesn't mean to go make sure everyone in the world is saved, but to me means, making others like the twelve He had picked to start His church.
Having the gospel preached to you and being a disciple are two vastly different things. Being a disciple, means to follow the disciplines put forth by Jesus Himself.
I think so many people have taken this passage and used it to go to every nation, having crusades, and alter calls to get people "saved", while overlooking the true meaning of the passage, to make disciples of all nations.
I think of the old parable, give a man a fish he will be fed for the day, teach a man to fish he will never go hungry, Jesus told Peter follow me and I will make your fishers of men.
I believe the Great Commission is for us to teach them to be like Jesus not just getting saved.
18 And Jesus came and spoke to them, saying, “All authority has been given to Me in heaven and on earth. 19 Go therefore and make disciples of all the nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, 20 teaching them to observe all things that I have commanded you; and lo, I am with you always, even to the end of the age.” Amen.