Since the word missionary was not used in the Bible, different people have defined who a missionary is at different times based on the perspective of thinking. A missionary is called and sent by God with a specific mandate to a particular people. A missionary is called by God to take the gospel of the kingdom of God to people that have not received it. The Bible tells of different individuals and groups of people who were called at different times to fulfill a missionary mandate. In the Old Testament it was God the Father who played the role as sender of missionaries for example, Abraham was called by God as an individual:
The Lord had said to Abram, “Leave your country, your people and your father’s household and go to the land I will show you” (Genesis 12:1). Israel as a nation was also called during this era: “You will be for me a kingdom of priests and a holy nation. These are the words you are to speak to the Israelites” (Exodus 19:6). God the Son was the sender of missionaries during the gospel period or the Pre-Pentecostal period and the call was specifically to the disciples who were also referred to as ‘Apostles’ from which the word missionaries emanated, “Therefore go and make disciples of all nations…” (Matthew 28:18)
Since the Apostolic or the Post-Pentecostal era, the responsibility of the sender shifted to God the Holy Spirit whose target became the church. The Holy Spirit calls the church today either as a group or individual to fulfill God’s missionary mandate.
“In the church at Antioch there were prophets and teachers: Barnabas, Simeon called Niger, Lucius of Cyrene, Manaen (who had been brought up with Herod the Tetrarch) and Saul. While they were worshiping the Lord and fasting, the Holy Spirit said, ‘Set apart for me Barnabas and Saul for the work to which I have called them” (Acts 13:1-3).
A missionary sender is simply an individual or a group that facilitates the fulfillment of God’s missionary mandate upon an individual or a group through spiritual and physical supports. It is God that calls and sends a missionary but He also needs men as co-senders. They are people who release the missionaries into their mandate through their prayers, financial, material and moral support. In the case of Abraham, his father, Terah, was the only person who was involved in his call, the prophets and priests served to help Israel fulfill her mission mandate. The church served as co-sender with God to help the Apostles fulfill their missionary call during the apostolic era. Today, the concept of co-sender’ with God in missionary task has become more developed and well structured in modern missions. Local churches act as ‘senders’, individual believers or group of believers act as senders, family members and sending organization act as senders and so on. It is this concept that brings about the fact that every believer is a missionary, either you are called to go as a missionary or called to serve as a co-sender with God.
The concept of unreached people is very fundamental in the modern day missionary work. Unreached people is defined as any group within which there is no indigenous community of  Bible believers able to evangelize this people group without  help or support from outside. An Unreached people group has an insignificant percentage of Christian evangelicals among them. We have majority of unreached peoples in Africa, and most of them are in the Islamic settings. There are still some unreached people in the world today that do not have missionaries among them yet. How then can we say that we have finished the task and how can we expect the Lord to return. The task is ‘to make disciples of all nations’, which means to raise and nurture believers among every tribe. We must speed up the fulfillment of our missionary task for we cannot expect the Master to come, until the whole world has heard the Good News.
God bless you,
Matthew Olorunnaiye.