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In Joshua 6 - we see the children of Israel facing a "closed" city. In fact, this city is large, fortified, and a formidable military opponent. Yet we see the Lord has commanded the city of Jericho to be destroyed and it will be done in a supernatural manner. The use of a great military force by Israel is unnecessary and in fact, the method employed by Israel is contrary to sound military advice.
With this said, Jesus has commanded us to go forth into all the world and preach the gospel. Is there such a thing as a "closed" nation when God has commanded us to go everywhere - even to the utter most parts of the earth? As a missionary to Africa - I know of areas that are hard to reach and closed to traditional methods of outreach. It is these areas I believe we can expect the supernatural power of God as seen at Jericho to again be prevalent. Three times in the book of Joshua the LORD speaks and says, "I have given".
It may take some imagination and courage - but I believe the Lord "has given" us a command to reach all people, nations, tongues, and tribes. In that giving of the command - our Lord has equipped us supernaturally to open that which is closed!