God told 1st century christians to preach. When he did that he was speaking to each individual. IMHO - we all have the burden placed on us in the Bible to share what we have learned about him and his son Jesus. I do not believe we need to be part of an organization to share this information with people though. We have the Bible just as Jesus and his disciples did.
Heck, allot of us here on this very site are sharing what we believe to be truth from the Bible. It doesn't come from a manmade organization. It comes from a personal study of the Bible in conjunction with God's Holy Spirit. Why should we preach what comes from man though?
I'm tellin' you. Read "Crises of Conscience" and you will see that the Society has not preached what comes from God. They have preached personal opinion, personal interpretation and double standards. They make no apologies when their past opinions have ruined people's lives and not for the sake of God's word but for the sake of the Organization maintaining a reputation as God's faithful and discreet slave.
The Bible IMHO is the only source we need to be able to preach God's word and many people are using it without having to be in a specific church.
In chapter Matthew 10 Jesus was speaking to his apostles. He continued on to tell them to not only preach but to cure sick people, raise up dead and expel demons. This scripture is being directed to the apostles and not to us. It applied to his time.
In Luke 4:19-21 Jesus said he had fulfilled the preaching work.
In Acts 10:34 -43 Peter is speaking about those that witnessed Jesus' resurrection. He ordered them to preach. Again, not speaking about us.
In Romans 10: 8 its says "The word is near you, in your own mouth and in your own heart:, that is the "word" of faith, which we are preaching." It doesn't come from a manmade source. It is in our hearts. That is what we preach.
In 1 Corinthians 1:22-31 it talks about preaching and emphasizes that "God chose the foolish things of the world, that he might put the wise men to shame; and God chose the weak things of the world, that he might put the strong things to shame". It doesn't say he chose a worldwide organization. One that is strong and powerful. He chose everyday individuals who were weak and foolish.
In 1 Corinthians 2:1-5 it is explained that "what I preached were not with persuasive words of wisdom but with a demonstration of spirit and power, that your faith might be, not in men's wisdom, but in God's power"
There are so many more scriptures that speak of preaching and it's purpose, etc. In my opinion, most of them have already seen their fulfillment. None of the scriptures above indicate the information used to preach came from a worldwide manmade organization or that you must be in a certain religion to preach God's word.