A missionary is “one who is sent.” Romans 10:14-16 shows us the purpose of sending. Specifically, it is one who is sent to tell people what God has said so that they may believe and be saved from eternal separation from God. Faith comes by hearing the word of God which is spoken by messengers who are sent. Jesus said, “As the Father has sent me, so send I you.” (John 20:21) In that sense, every Christian is “sent.”
Until recently, in Bible-believing churches, “missionary” has meant a person sent by the local church on a journey to accomplish the Biblical mission or objective of proclaiming the glory of Christ where there has been no Gospel witness. “Teaching people to observe all” that Christ commanded includes discipleship. “Missionary” work has been driven by “The Great Commission” given by Jesus, following a central theme of the entire Bible, that is recorded in Matthew 28:16-20 (all ethnos), Mark 16:15 (every creature), Luke 24:46-48, Acts 1:8, 1 Corinthians 15:34, and 2 Corinthians 5:10-20.
The primary role models for career “missionaries” have been Paul and Barnabas, who, while working to minister as part of the local church in the community of Antioch, were set apart by the Holy Spirit, the local church leaders, and the community of believers there to proclaim the Gospel and establish local churches in places where Jesus Christ has been unknown. (Acts 13:1-3)
The historical concept of a Biblical missionary is that of people who have been sent by local churches to people who had no access to the Gospel. Many others traveled to assist. Timothy stayed to equip.
Every Christian should have a part in what God is doing globally. Missions efforts require the whole body. There are roles in pioneering new ministry where Christ is unknown, in teaching established churches until they reach maturity, in supporting the Bible teaching missionaries through physical means, in preparing missionaries for effective service, in overseeing the ministries of the teams, in providing infrastructure to enable teams to function well, in keeping donors aware of progress and needs, and in sending from churches.