Reducing ideas down to some manageable level is part of surival in life. Strategic reduction is needed to accomplish any task. It involves identifying the core tasks or core ideas, and minimizing or eliminating from one's mind or mazeway the many miriads of details in order to cope with those core ideas. It is part of theory building, this capacity to identify ideas and build them into themes then into theories, which only approximate reality as we have cut out everything else. Electical engineers when describing radio signals call this "white noise" - good noise, but it is not necessary and makes the crucial signals less easily discernible.
Scholars thus identify what they have ignored, while affirming the core truths they hold. Those not trained in scholarship often delight in a narrow understanding of "truth". What they perceive as right is right!! And all who declare otherwise are to be condemned in loud angry voices!! this leads to what is generally termed as religious fundamentalism, which includes an anti-intellectualism and a diviseness - be it Islamic or a form of Christianity. Rural populations in mono-ethnic societies tend to be more fundamentalist as they have not significantly encountered diversity, so have not developed skills to engage with a breadth of ideas divergent from what they perceive as truth.
We understand that God is truth and that in the Bible we have "divinely inspired" truth. There are some who go further and believe that their understanding of the scriptures is truth. James 3:14-16 tells us that wisdom is open to reason, to be humble and considerate. Christ is our wisdom. He integrates all in all. So we are to be filled with the Spirit of wisdom, and seek to understand how he sustains every structure of the universe, every node of integration. But humble in that our perception may not have been always accurate. That is the field of theology, to test truth against historic understandings of the scriptures, and against understandings today across the globe. There are criteria in every discipline for determining truth in that field of knowledge. In theology there are numerous principles that are also followed.
Some like to reduce missions to church growth and evangelism. Some in "liberal" wings of the Protestant church like to reduce it to social action without direct evangelism - which is seen as offensive. Holistic mission instead affrims both of these poles and seeks to integrate them.
William Carey was known as the father of Protestant missions. He evangelized in West Bengal, planted churches, and a Seminary, but also set up a University, studied botany, formed a botanical society, published literature on culture and language, fought for the abolition of suttee (the burning of the widows of the dead), etc. He understood that the preaching of the good news of the Kingdom influenced all areas of life. it cannot be simple for the simple but not reductionist.
The US Center of World Missions has also focussed on church growth in "people groups" and this has proven AN effective strategy. But it has reduced out other factors that make it of less significance in cities. It is a very significant strategy when dealing with migrants moving into the city, but less useful as people integrate into the city. It has foucussed onto the least smallest unevangelized tribe, who are important, but meanwhile the tribes have moved to the cities. Cities must be reached as both cities and as clusters of people groups, as neighbourhoods and as networks. Thus a reductionist strategy has hindered the focussing of resources onto the great movement of God in urban migration. A holistic strategy is needed, that engages both peoples and cultures, systems and structures, places and networks, urbanism and the urban people -tribal people, peasant enclaves in the city, socio-economic regions, the rich, the poor, and postmodern youth.