This is a most fundamental question, which should not be answered lightly. My goal as usual, the Lord empowering, is to pluck the 21st century believer out of the muck of the 21st century popular culture of Christianity, that neutralized insipid shadow of a faith; into the realm of the eternal Bride of Christ.
Who we are Not
The popular culture, (drowning in the sewers of secularism as it is), emphasizes the demand for blessings over the joy of suffering. Thus, creating wimpy, couch potato believers- unwilling and unable to lift a finger for the cause of Christ. It elevates fleeting feelings and empty sincerity over absolute truth; creating pacified, shapeshifting, people pleasers- who, ironically, care about everyone's feelings except God's.
This culture sustains spiritual infancy, blunts spiritual hunger, ties the heart to the physical world blinding the eyes to the supreme realities of the eternal realm. Malnourished believers thus enamored by the culture end up tossed by every wind, deep as a trickle, bright as a shadow, salty as sugar itself.
This disease of a worldview seduces the believer, in the midst of war on every side, to lay down his sword and shield and enter the make-believe world which sees him lounging on the playground, instead of in battle. This is the secular trance. It cloaks the depth of the family into which we have been grafted and leaves us instead with a list of activities devoid of history, identity and purpose.
Contemplating evangelism as the answer
What then is the true role of the church in the world? I humbly submit, answering with a verb "to do this" or "to do that" does not do justice to God's eternal project, nor can it contain the glorious bride. Many will say, "to evangelize" citing "the Great Commission". Though the preaching of the gospel of the good news is definitely necessary, I do not see it as solely sufficient to grasp the fullness of God's vision for the existence of the church.
I commend all missions organizations, evangelistic initiatives and organizations geared to the salvation of souls as doing wonderful work. However, the reality is that while preaching the gospel of the cross brings sinners to repentance and new birth in Christ, it does not mature these newborn spiritual babes.
If the role of the church is primarily evangelism, then the ideal demographic of the church is that of newborns. Will the Lord marry an infant and immature bride? It is instructive that Jesus gave, the call to also "make disciples, [how?] teaching them to obey everything I have commanded". (Matthew chapter 28 verse 19).
I submit to us that this dear passage stretches the role of the church far past the point of spiritual birth to spiritual fullness and maturity.
Wider and deeper still
Though many individuals will find their purposes fully enveloped in evangelism, there is more to the church than that, just as there is more to the body than the office of the evangelist. “Christ himself gave the apostles, the prophets, the evangelists, the pastors and teachers, to equip his people for works of service... so that we may become mature, attaining to the whole measure of the fullness of Christ. Then we will no longer be infants” (Ephesians chapter 4 verses 11-14).
Now we have found five offices, evangelism being purely outward focused, teaching and apostleship being internally focused and prophecy functioning on both plains, all with the aim of maturity.
I think we have established more of the width of the calling we have received, so we are surely getting warmer. However, at our core as the Bride of Christ must be a deep-seated, love-grounded identity and the focus of purpose. Indeed, the concept of an activity-based identity, rather than a relationally based identity, contributes to a level of superficiality and accentuates the inadequacy of these important offices to fulfill the role of a core identity.
Where does that leave us?
I submit to us the Lord's official first interaction with his people in Exodus chapter 19 verse 4, he calls the family into which we have been grafted " a kingdom of priests, a holy nation". This sentiment is echoed in Revelation chapter 1 verse 6 which reads: "Unto him that loved us, and washed us from our sins in his own blood, and hath made us kings and priests unto God".
Having been brought into the family of God as sons and daughters, we are kings and queens, a royal priesthood, who operate out of deep-rooted love for the Father. This, I submit rings with the depth of relational identity, the weight of history, the expressed dream of God fastened to the strength and focus of purpose; which other answers to the question “What is the role of the Church?” do not give.
Now, what does it mean to be kings and priests?