The essence of the gospel is to reach out to the unsafe. This is why the early apostles went about from city to city preaching the gospel. This is mission to  unreached peoples.  Today, there is high concentration of churches in most cities, which is commendable but there is an important aspect of the ministry which involves reaching out to areas were the gospel has not been reached.
Apostle Paul measured in this capacity.

Text: Romans 15:20
It has always been my ambition to preach the gospel where Christ was not known, so that I would not be building on someone else’s foundation. It is a higher responsibility to reach those not reached, but it is easier to build on someone else foundation. Many workers in the vineyard of God are in their comfort zone. While some are resting on their oars.

God is highly interested in the mission of spreading the gospel to nations where the gospel has not been preached. This is why God allowed persecution to the early Church which served as catalyst to the spread of the gospel. Yes! In an attempt to escape the persecution, they ran to far nations and they preached the gospel along reaching the  gentiles.

Remember the gospel must be preached to all nations before the Jesus Christ will come. Mathew 24:14 And this gospel of the kingdom will be preached in the whole world as a testimony to all nations, and then the end will come. We might facilitate his coming by fulfilling this condition by embarking on mission to unreached peoples.
Therefore the church should focus more of her evangelism in reaching nations where the gospel has not been preached.
According to the  JOSHUA PROJECT, there are about 1510 ethnic groups which have not been reached. which means that no church, no missionary, no mission agency…no one has yet taken responsibility to tell them about Jesus Christ.

Every Christian has a role to play in carrying the gospel to the unreached peoples of the world. This can be done by individual or corporate effort through:
1. Embark on a mission project
2. Contributing  to fund missionary projects to these ethnic groups.
3. Pray for missionaries

You can also check out The great commision of soul winning.
Source www.restforall.com