To discuss the role of foreign missionaries in the 21st century, we first have to define some terms.
I will define missionary as a believer in Jesus Christ who desires to share the good news of Jesus Christ (I will later use the term gospel).
A foreign missionary (according to the definition for this article) is a missionary who crosses cultural and national borders (for example: an American moving to Taiwan for the purpose of sharing the gospel).
A role includes the long-term purpose and subsequent practical work to get to that purpose.
In previous eras, foreign missionaries have obeyed either God, scripture, or both and went to a foreign place to give a new people group a chance to hear and believe the gospel.
At first, of course, this always entailed going into a place where there were no believers or churches at all, but over time it involved more of a strengthening, equipping, and continuation of previously established work.
If you enter a country that has no deeply established churches, then there is an obvious need to establish believers into an organized body so that they can function according to scripture.
A country with a long history of revivals (many people coming to faith in Jesus) and evangelism is always adjusting their methods to fit the new historical context they find themselves in.
Foreign missionaries can see areas for change that people within that context may be blind to and therefore help to strengthen the church by replacing ineffective methods with effective methods.
Surprisingly, you can go into a country with 5% (or less) Christians and still find that there are strongly established churches that autonomously function to evangelize, disciple, and care for Christian believers.
I want to focus this discussion on these places that have healthy communities of believers yet most of the population do not believe the gospel.
In this example, the local believers are definitely doing all the things required of a church and yet they are not yet seeing the break-through experienced in other places.
So what purpose does a foreign missionary have in such a context?
First, I do not believe it involves starting something new because that would deny the truth that there are already healthy established believing communities.
I also don't believe they should promote themselves into a high position within the church structure to make subsequent changes.
The ultimate purpose should be the same as that found in Matthew 28:19-20 and Ephesians 4:12-13:
Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all that I have commanded you. And behold, I am with you always, to the end of the age.
For building up the body of Christ, until we all attain to the unity of the faith and of the knowledge of the Son of God, to mature manhood, to the measure of the stature of the fullness of Christ.
Personally, I believe there are two major functions that a foreign missionary can move into to see this purpose fulfilled.
The first is offering their unique viewpoint from an outsider position that can help discover and remove barriers set up by the church that actually work against the spread of the gospel.
At this point I must stress that we must first understand the culture and the local church before we insist we are right and they are wrong.
A humility is required to bring correction and it must be done in love.
The second is Spirit-led prayer.
With language and cultural inefficiencies, you cannot expect to minister more clearly and effectively than a local leader, but you can be used by the Holy Spirit as a vessel to bless the church.
Praying (especially in tongues, for example) transcends language inadequacies and can inspire others to surrender fully to God.
Practically, these two areas are about Word and Spirit.
On one side, you have to communicate a clear correction or vision for the church.
On the other, you have to actively pray for the church and serve in faith empowered by the Holy Spirit.
The church is a body and each member has a function and gifting from God.
Each of us must submit to God, have faith, and be obedient to God's word(s).
For as long as you are a missionary on the foreign field, I encourage you in these areas for the building up of the church and the discipling of nations.
All glory to God.